| Type: | Package |
| Title: | Time Series Costationarity Determination |
| Version: | 2.4.1 |
| Date: | 2023-09-06 |
| Depends: | R (≥ 2.14), wavethresh (≥ 4.6.1) |
| Suggests: | parallel |
| Description: | Contains functions that can determine whether a time series is second-order stationary or not (and hence evidence for locally stationarity). Given two non-stationary series (i.e. locally stationary series) this package can then discover time-varying linear combinations that are second-order stationary. Cardinali, A. and Nason, G.P. (2013) <doi:10.18637/jss.v055.i01>. |
| License: | GPL-2 | GPL-3 [expanded from: GPL (≥ 2)] |
| NeedsCompilation: | no |
| Packaged: | 2023-09-06 14:08:43 UTC; guynason |
| Author: | Guy Nason [aut, cre], Alessandro Cardinali [aut, ctb] |
| Maintainer: | Guy Nason <g.nason@imperial.ac.uk> |
| Repository: | CRAN |
| Date/Publication: | 2023-09-06 21:32:33 UTC |
Computes localized autocovariance and searches for costationary solutions to bivariate time series.
Description
Computes a time-varying autocovariance and associated plots for plotting this. Also can search for costationary solutions between two time series.
Details
See findstysols for help page for main function.
Author(s)
Guy Nason, <g.nason@imperial.ac.uk>
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# Compute localized acv
#
x <- c(rnorm(128, sd=1), rnorm(128, sd=3))
xlacv <- lacv(x, lag.max=30)
#
# Plot the time-varying autocovariance at time t=100
#
## Not run: plot(xlacv, type="acf", the.time=100, plotcor=FALSE)
#
# Plot the time-varying autocovariance at time t=400
#
## Not run: plot(xlacv, type="acf", the.time=400, plotcor=FALSE)
#
# See examples for findstysols for other examples
#
Undo autoreflection action for an EWS object (wd stationary)
Description
The BootTOS function has the ability to
deal with boundary conditions by augmenting the right-hand end of a time
series by a reflected version of that series. So, the series doubles
in length and the new vector has periodic boundary conditions. One
can then compute a local spectrum on this data which returns an EWS
in a wd object, usually with a type attribute of "station".
This function can take this wd object and properly can return
the first half of it, which corresponds to the boundary-correct spectrum
of the original series.
Usage
AntiAR(S)
Arguments
S |
A |
Details
This function arises because using spectral estimation functions,
like ewspec from the wavethresh package doesn't
always work that well at the boundaries. This is because
the wavelet functions in wavethresh usually assume
periodic boundary conditions and this is not appropriate for
a discrete time series where time 1 and time T are usually
very different (and cannot be assumed to be the same).
Hence, a previous function could generate a new time series by taking the
original, e.g. x, reflecting it with rev(x) and then
sticking the reflected onto the right-hand end of the original.
Spectral estimation, (e.g. using ewspec) can then be applied
to this new reflected/augmented series and the boundaries are now
roughly correct as the start and end of the series correspond to time 1.
The spectral estimate so obtained though is double the size of the the one that is needed, and contains the spectrum of the reflected series. Hence, this function obtains the first half of the estimate and returns it.
Not usually intended for the casual user
Value
A wd class object containing the boundary-corrected
estimate of the spectrum for the original series.
Author(s)
G. P. Nason.
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# Generate example, temporary series
#
x <- rnorm(128)
#
# Reflect it about its end point
#
x2 <- c(x, rev(x))
#
# Compute EWS estimate
#
x2ews <- ewspec(x2)
#
# Now get bit corresponding to x into object
#
xews <- AntiAR(x2ews$S)
Perform bootstrap stationarity test for time series
Description
Given a time series this function runs a bootstrap hypothesis test to see whether it is stationary. The null hypothesis is that the series is stationary, the alternative is that it is not - and hence possesses a time-varying evolutionary wavelet spectrum if deemed non-stationary.
Usage
BootTOS(x, Bsims = 100, WPsmooth = TRUE, verbose = FALSE, plot.avspec = FALSE,
plot.avsim = FALSE, theTS = TOSts, AutoReflect=TRUE, lapplyfn=lapply)
Arguments
x |
Time series to test. Must have a power of two length |
Bsims |
Number of bootstrap simulations to carry out |
WPsmooth |
Whether or not to carry out wavelet periodogram smoothing |
verbose |
If |
plot.avspec |
If |
plot.avsim |
If |
theTS |
Specifies the particular test statistic to be used |
AutoReflect |
If TRUE then the series is reflected and augmented by its end point on the RH-side, and the spectral quantities are evaluated on that. Everything returned though applies only to the original series, the reflection is merely to ensure that the periodic wavelet algorithms can be used on non-periodic data |
lapplyfn |
List processing function. Parallel processing of
the bootstrap simulations can be achieved by using the |
Details
The details of our testing methodology are set out in the Cardinali and Nason paper referenced below.
Essentially, the testing process works as follows. First, one
has to define a test statistic. Given a time series this has
return a statistic that measures ‘degree of nonstationarity’.
For example, estimating the EWS, and then computing the
sum of the sample variances of each scale is such as
measure (and known as the T_{vS} statistic).
This statistic is zero for a constant spectrum and positive
for non-constant spectrum (and generally larger for larger variations
of the spectrum).
Once a test statistic T is selected then a parametric Monte Carlo
test can be used. First, T is computed on the series itself.
Then, for statistical assessment of the ‘significance’ of the test
statistic the following procedure is carried out. Assuming, for
a moment that the time series is stationary, we estimate its
evolutionary wavelet spectrum (EWS) and then average this over
time (\bar{S}_j). Then we use the function
LSWsim to simulate a time series whose EWS is the
constant, stationary, spectral estimate. Then we compute our
test statistic, T_b, on this simulated series.
Then we calculate T_b for Bsim-1 simulations. The function
then returns BSim numbers. The first is the test statistic
computed on the actual data. The remaining ones are the test
statistic computed on the simulated stationary series.
The idea being that if the time series is really stationary then the first value will be comparable to the ones obtained by simulation. If the time series is not stationary then the first test statistic will be much larger than the ones obtained by simulation (since the actual data T will have been computed on a time series with varying spectrum, whereas the simulated ones are all computed on constant spectra, and their variation is only due to sampling variation).
The test statistic supplied to this function (as argument
theTS) should take an EWS object as an argument.
For example, the WaveThresh function ewspec
produces a suitable spectral estimate in its $S
argument (both objects are actually examples of a
non-decimated wavelet transform object, class wd).
The function plotBS can be used the present the results
of this function in an interpretable form and calculate the
p-value of the test, although you should use the
generic plot function to call this.
Value
A vector of length Bsim. The first entry is the value
of the test statistic computed on the data. The remaining
entries are boostrap values computed on the ‘averaged’ EWS estimate
with constant spectrum.
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# Calculate test of stationarity on example we know to be stationary,
# a series of iid values
#
plot(BootTOS(rnorm(64), Bsims=10), plot=FALSE)
#
# The following text is what gets printed
#
#Realized Bootstrap is 0.04543729
#p-value is 0.93
#Series was stationary
#[1] 0.93
#
# The realized bootstrap value is the value of the test statistic on the
# actual data (0.0454 here).
#
# The p-value is also printed (this is just the number of simulated series
# test statistic values less than the actual test statistic) and returned.
#
# The text "Series is stationary" just means that the empirical p-value
# was greater than the nominal test size (alpha=0.05, by default).
#
# Let's now try another example with the series sret: note that if you
# have a slow single core machine, this can take a long time, so we don't
# run it in the examples. However, on a fastish machine it is quick, on
# a fast multicore machine it is really quick!
#
## Not run: plot(BootTOS(sret))
#
#Realized Bootstrap is 2.662611e-09
#p-value is 0
#Series was NOT stationary
#[1] 0
#
# In contrast to the previous example, the p-value is 0, hence indicative
# of non-stationarity.
#
Produces plots from output of findstysol that attempt to group different solutions.
Description
Uses hierarchical clustering and multidimensional scaling to produce a plot of all the convergence stationary solutions. These plots are designed to aid the user in identifying ‘unique’ sets of stationary solutions.
Usage
COEFbothscale(l, plotclustonly = FALSE, StyPval=0.05, ...)
Arguments
l |
An object returned by |
plotclustonly |
If |
StyPval |
The p-value by which solutions are deemed to be
stationary or not for inclusion into plots. If the p-value
for a particular solution is greater than |
... |
Additional arguments to the hierarchical clustering plot. |
Details
The function findstysols uses numerical
optimization to try and discover time-varying linear combinations
of two time series to find a combination which is stationary.
Like many numerical optimizations the optimizer is supplied with
starting coordinates and proceeds through an optimization
routine to end coordinates which are located at the minimum
(in this case). So, the user has a choice over where to start
each optimization.
A priori there is no recipe for knowing where to start the optimizer, so such situations are usually handled by running the optimizer many time each time starting in a different position. The solution here is to start from a set of different randomly chosen starting points. After the optimizer is run from these different starting positions it ends up in the same number of potentially different ending positions.
However, some of the ending solutions might be identical, some might be very close, some might be reflections (e.g. the if the coefficients (a,b) result in a stationary solution then so does (-a, -b)). Morally, though, all of these cases would reference the same solution.
Hence, we require some method for identifying the set of unique solutions. We can be considerably aided in this task by multidimensional scaling (which uses inter-solution distances to produce a map of how close solution sets really are) or hierarchical clustering (which can produce a nice picture to indicate how the solutions might be related).
In other words, the solution vectors can be viewed as a multivariate data set where the cases correspond to the results of different optimization runs and the variables correspond to the coefficients of the time-varying linear combinations.
Both multidimensional scaling (cmdscale) and
hiearchical clustering (hclust) are used to determine
possible clusterings of solutions. Then, representative members
from these clusters can be further investigated with a function
such as LCTSres
Value
An object of class csFSSgr is returned containing the
following components: the results of the multidimensional scaling
and hierarchical
clustering are returned as list with two components
epscale and epclust respectively, and
the input l object is returned as component x
and the StyPval object is returned as a component.
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# See example in findstysols
#
Perform running mean smoothing of an EWS object
Description
Performs running mean smoothing of bandwidth s of
an EWS, such as that returned by the ewspec function
of wavethresh.
Usage
EWSsmoothRM(S, s)
Arguments
S |
The spectrum to smooth |
s |
The bandwidth (or number of ordinates to include in the running mean) |
Details
Each level of the EWS is subject to a running mean smooth. After smoothing a level the resultant smooth is shorter than the original level (due to the mean not being able to overlap the boundaries). This deficit is made up by augmenting the start of the smooth with a right number of smoothed values taken from the first smoothed value.
Value
A EWS object contained in a wd object of type "station"
which contains the smoothed spectrum.
Author(s)
G.P. Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# Make dummy time series
#
x <- rnorm(128)
#
# Compute spectrum, but don't do smoothing
#
xews <- ewspec(x, WPsmooth=FALSE)$S
#
# Now smooth the spectrum using running mean smoothing with bandwidth of 5
#
ans <- EWSsmoothRM(xews, s=5)
Computes a Linear Combination Test Statistics
Description
Given a particular linear combination, specified in terms of coefficients, cfs, this functions forms the linear combination of two time series, tsx, tsy and returns the result of a stationarity test statistic on the combination.
Usage
LCTS(cfs, tsx, tsy, filter.number = 1,
family = c("DaubExPhase", "DaubLeAsymm"), plot.it = FALSE,
spec.filter.number = 1,
spec.family = c("DaubExPhase", "DaubLeAsymm"))
Arguments
cfs |
Coefficients describing the linear combination vectors. The first half correspond to the first vector (alpha) the second half to the beta vector. Hence this vector must have an even length, and each half has a length a power of two minus one. |
tsx |
The x time series |
tsy |
The y time series |
filter.number |
This function turns the coefficients into a linear combination function (e.g. alpha). This argument specifies the filter.number of the inverse wavelet transform that turns coefficients into a lc function. |
family |
Same as filter.number but for the wavelet family |
plot.it |
If TRUE then various things are plotted: both of the linear combination vectors/time series, the combined time series and its EWS estimate |
spec.filter.number |
The wavelet filter used to compute the EWS estimate |
spec.family |
The wavelet family used to compute the EWS estimate |
Details
This function forms a time-varying linear combination of two
times series to form a third time series. Then a 'stationarity
test' test statistic is applied to the third time series to
compute how stationary (or non-stationary it is). This function
is called by findstysols and actually does the work
of forming the lc of two time series and gauging the stationarity
Value
A single number which is the value of the test of stationarity
for the combined time series. This is the result of TOSts
but normalized for the squared coefficient norm
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# Apply this function to random combination coefficients.
#
# The combination coefficients: comprised of two vectors each of length 3
# Note that 3 = 2^2 - 1, vectors need to be of length a power two minus 1
#
# sret, fret are two time series in the package
#
data(sret)
data(fret)
LCTS( c(rnorm(3), rnorm(3)), sret, fret)
#[1] 1.571728e-13
#
# The value of the test statistic is 1.57e-13
Plots solutions that are identified by findstysols
Description
Plots lots of useful information concerning solutions identified using findstysols. It only plots those where the optimizer converged. Can additionally return the time-varying linear combination associated with any solution if plots are turned off.
Usage
LCTSres(res, tsx, tsy, inc = 0, solno = 1:nrow(res$endpar), filter.number = 1,
family = c("DaubExPhase", "DaubLeAsymm"), plot.it = FALSE,
spec.filter.number = 1,
spec.family = c("DaubExPhase", "DaubLeAsymm"), plotcoef = FALSE,
sameplot = TRUE, norm = FALSE, plotstystat = FALSE,
plotsolinfo = TRUE, onlyacfs = FALSE,
acfdatatrans = I, xlab = "Time", ...)
Arguments
res |
Solution set returned by findstysols |
tsx |
The |
tsy |
The |
inc |
Adds an increment to the x-axis values. |
solno |
Which solution number to look at. This can be a vector of solution numbers. The default is to look at all solutions (which can be a lot, depending on how many you've got) |
filter.number |
The wavelet filter number to use in reconstructing the linear combination function |
family |
The wavelet family to use in reconstructing the linear combination function. |
plot.it |
Currently unused in this function |
spec.filter.number |
This function computes the linear combination
time series and also then computes its EWS.
The wavelet ( |
spec.family |
The family of the wavelet used to compute the spectrum |
plotcoef |
If TRUE then only the linear combination functions are plotted. If FALSE then a (set of potentially multiple) composite plot(s) are produced. These composite plots are what are usually most useful. |
sameplot |
If TRUE then the linear combination functions are plotted on the same plot. |
norm |
If TRUE then the linear combination functions are normalized
before plotting if |
plotstystat |
If TRUE (and if |
plotsolinfo |
If TRUE (and if |
onlyacfs |
Only plot the two acfs if |
acfdatatrans |
A function (e.g. |
xlab |
An x label for the time series plots, and spectral plots |
... |
Extra arguments for the acf plots. |
Details
The function findstysols takes two time series
and attempts to find time-varying linear combinations of the
two that are stationary. If one is found, we call it Z_t.
However, findstysols works by numerical optimization,
typically from random starts, and, generally, there is no unique
stationary solution.
This function takes the results obtained by findstysols
in an object called res and then for a set of solutions
already identifed by the user, and supplied to this function
via solno, this function takes each identified solution
in turn and produces a set of plots.
Determining which solutions are interesting is another problem.
The COEFbothscale is a useful function which
can analyze all solution sets simultaneously and, usually, arrange
them into groups which are mutually similar. Then representative
members from each group can be further analyzed by
LCTSres.
Probably the most useful set of options is
plotcoef=FALSE and to issue a
par(mfrow=c(2,2)) command prior to running
LCTSres. This produces the plots, four to a page,
and enables interesting features to be compared from plot to plot.
The plotcoef=FALSE option causes four plots to be produced
(on the same page if mfrow is set as the previous paragraph
suggests). The first two are the (potentially) time-varying linear
combination functions, the next is the stationary linear
combination, Z_t, itself and the final plot is an estimate of
the Z_t's evolutionary wavelet spectrum. The titles of the latter
two plots display the process variance of Z_t (the global
unconditional variance, because Z_t is assumed to be stationary)
and the p-value associated the the hypothesis test of stationarity
of Z_t. The spectral estimate show exhibit near constancy because
of the stationarity (as assessed by hypothesis test) of Z_t.
If plotstystat=TRUE then further plots are produced
of the results of various classical time series analyses of Z_t.
If onlyacfs=TRUE then only the acf and partial acf of Z_t
are plotted, otherwise Z_t and its classical spectrum are also
plotted (remember, Z_t, has tested to be stationary and so these
classical methods are valid).
If more than one solution is to be plotted, then the scan()
function is employed to pause the plots between plots.
Value
The stationary solution, Z_t, associated with the last solution
to be plotted is returned. Of course, if there is only one
solution to be plotted then it is the only possibility. Hence,
if all the plot arguments are FALSE then no plots are
produced and the stationary linear combination of the (last)
solution number is returned.
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# See examples in findstysols (the plot method for the results of
# findstysols make use of LCTSres)
Log-returns time series of the SP500 and FTSE100 indices
Description
Log-returns of the SP500 and FTSE indices between 21th June 1995 until 2nd October 2002. Only trading days where both indices were recorded are stored. There are 2048 observations.
Usage
data(SP500FTSElr)Format
A data frame with 2048 observations on the following 3 variables.
DateThe trading day that the index was recorded.
SP500lrThe log-return for SP500
FTSElrThe log-return for FTSE100
Source
Downloaded from Yahoo! Finance
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
Examples
#
# Plot the log-returns for the SP500
#
## Not run: ts.plot(SP500FTSElr[,2])
A test statistic for stationarity
Description
The T_{\mbox{vS}} test statistic from
the Cardinali and Nason article. Measures the degree of
non-stationarity using the estimated evolutionary wavelet
spectrum (EWS)
Usage
TOSts(spec)
Arguments
spec |
An EWS estimate, e.g. from the |
Details
Given an EWS estimate. This computes the sample variance of the estimate for each scale level and then returns the sum of these variances.
Value
A single number which is the sum of the sample variances of each scale level from an EWS estimate. If the EWS estimate is constant for each scale then the return value is zero.
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# Compute a spectral estimate on an sample time series (just use iid data)
#
xsim <- rnorm(128)
xews <- ewspec(xsim, smooth.dev=var)$S
#
# You could plot this spectral estimate if you liked
#
## Not run: plot(xews)
#
# Compute test statistic
#
TOSts(xews)
#[1] 0.1199351
#
# Although the time series x here is a realization from a stationary process
# the test statistic is not zero (this is because of the estimation error
# inherent in this small sample).
#
# This is why the bootstrap test, \code{\link{BootTOS}} is required to
# assess the significance of the test statistic value.
Convert wavelet coefficients for two time-varying functions into two functions with respect to time.
Description
In much of the costationarity code the combination functions are represented in terms of wavelet coefficients. At certain points the actual combination functions themselves are required (in the time domain) for purposes such as actually forming the linear combination. This function turns the coefficients, for the two combination functions, into their time domain functional representation.
Usage
coeftofn(alpha, beta, n = 256, filter.number = 1,
family = c("DaubExPhase", "DaubLeAsymm"))
Arguments
alpha |
One set of coefficients for one of the combination functions |
beta |
The other set of coefficients |
n |
The length of resulting function that you require |
filter.number |
The type of wavelet (the number of vanishing moments) |
family |
The type of wavelet (the wavelet family) |
Details
A degree of efficiency is built into the code. Typically, for forming stationary linear combinations then only a few (or at least a medium number) of coarser scale coefficients need to be manipulated (eg modified in the optimizer). However, the actual length of the function (time series length) is typically much longer (e.g. n=256, n=512, or higher). So, this function pads out the small number of coarse coefficients with zeros before forming the combination functions which end up at the correct length, n.
Value
An object of class csBiFunction which is
list containing two components:
alpha |
A vector, of length n, containing one of the time-varying combination functions |
beta |
Same as |
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# Very artifical example
#
tmp.a <- c(1, -1)
tmp.b <- c(0.5, 0.5)
#
#
#
ans <- coeftofn(tmp.a, tmp.b)
#
# Print it out
#
ans
#Class 'csBiFunction' : Contains two sampled functions:
# ~~~~ : List with 2 components with names
# alpha beta
#
#
#summary(.):
#----------
#Length of functions is: 256
Extractor function for csFSS object.
Description
Get much information from the slots of a csFSS.
Each slot can carry information from multiple solutions
per slot. This function permits an arbitrary selection of
solutions for information from a slot.
Usage
extractCS(object, slot=c("startpar", "endpar", "convergence",
"minvar", "pvals", "lcts"), coeftype=c("all", "alpha", "beta",
"alphafunc", "betafunc"), solno, ...)
Arguments
object |
The |
slot |
The slot that you want to get information on. These
are The |
coeftype |
For the slots that return coefficients, these can
be returned in various ways. Each coefficient vector (one per
solution) actually stores two sets of coefficients: one associated
with the alpha_t linear combination and the other with
the beta_t linear combination. Setting |
solno |
The indices of which solutions you want the information on |
... |
Other arguments to |
argument.
Details
Extracts slot information from csFSS objects.
Value
Information from the relevant slot, as a number, vector or matrix depending on what it is that is requested as described in the various arguments above.
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# Create dummy data
#
x1 <- rnorm(32)
y1 <- rnorm(32)
#
# Find stationary combinations
# Note: we don't run this example in installation/package formation as
# it takes a long time. However, this precise command IS run in
# the help to findstysols
#
## Not run: ans <- findstysols(Nsims=100, tsx=x1, tsy=y1)
#
# Get the optimal (endpar) alphas for the first 10 solutions
#
## Not run: extractCS(ans, slot="endpar", coeftype="alpha", solno=1:10)
#
# Plot the beta_t associate with the optimal solution for solution 29
#
## Not run: ts.plot(extractCS(ans, slot="endpar", coeftype="betafunc",
solno=29))
## End(Not run)
#
# Get the p-value associated with solution 29
#
## Not run: extractCS(ans, slot="pvals", solno=29)
Given two time series find some time-varying linear combinations that are stationary.
Description
Find some time-varying linear combinations of two
time series that are stationary. The complexity of the
time-varying combinations is restricted by the Ncoefs
argument.
Usage
findstysols(Nsims = 100, Ncoefs = 3, tsx, tsy, sf=100, plot.it = FALSE,
print.it=FALSE, verbose = FALSE, lctsfn=LCTS, prodcomb.fn=prodcomb,
filter.number=1, family=c("DaubExPhase", "DaubLeAsymm"),
my.maxit=500, spec.filter.number=1,
spec.family=c("DaubExPhase","DaubLeAsymm"),
optim.control=list(maxit=my.maxit, reltol=1e-6),
irng=rnorm, lapplyfn=lapply, Bsims=200, ...)
Arguments
Nsims |
Number of searches attempted |
Ncoefs |
Number of Haar wavelet coefficients to use. Must be >= 1. Should only increase in steps of powers of two. E.g. can only supply the values 1, 3, 7, 15, etc. So, "1" means only one coarse scale coefficient (corresponds to piecewise constant with one centrally located jump), "3" means one coarse, and two next coarse scale coefficients (corresponds to piecewise constant with 4 equally sized piece with jumps at 1/4, 1/2 and 3/4), "7" means one coarse, two next coarse, four next coarse, and so on. |
tsx |
One of the time series |
tsy |
The other time series, values at the same time locations
as |
sf |
A scale factor to multiply both time series by (not really of much use) |
plot.it |
If |
print.it |
Not currently used in this function, reserved for future use |
verbose |
If |
lctsfn |
The function to compute the 'linear combination test of stationarity'. I.e. it is the function that combines the two series and returns the value of the test statistic on the combination. |
prodcomb.fn |
The function that can produce the linear combination of the two time series and return the combination, and optionally vectors containing the combination functions. |
filter.number |
Gets passed to |
family |
Gets passed to |
my.maxit |
Maximum number of iterations in the optimization. May need to be increased to, e.g. 1000 or 2000 for longer time series (e.g. T=2048) |
spec.filter.number |
Wavelet filter number. This argument
gets passed to the |
spec.family |
Same as |
optim.control |
Argument passed to the |
irng |
Random number generator used to generate coefficients for starting parameters for the linear combination of time series (actually wavelet coefficients of the combination functions) |
lapplyfn |
Function to use to process lists. If this argument
is |
Bsims |
The number of bootstrap simulations for the (single)
test of stationarity |
... |
Other arguments, passed to the |
Details
The function searches for time-varying linear combinations of
two time series, tsa and tsy, such that the combination
is stationary (according to the TOSts test statistic).
Each linear combination is parametrised by a coarse scale
Haar wavelet decomposition (controlled by Ncoefs).
Initially, the Haar wavelet coefficients (up to a fixed finite scale,
controlled by Ncoefs) are randomly chosen. These coefficients
are converted to functions \alpha_t, \beta_t
by the coeftofn function and then a linear combination
with the time series is formed out of those and the time series,
i.e.
Z_t = \alpha_t x_t + \beta_t y_t
The non-stationarity of Z_t is measured using the
TOSts test statistic and this value is minimized
over the coarse scale Haar wavelet coefficients.
This optimization procedure is repeated Nsims times.
If the lapplyfn is set to mclapply then this
function from the multicore package is used to process
the lists in parallel.
This function can be called multiple times (e.g. on different
processors in a multiprocessor environment. The result sets from
different runs can be combined using the
mergexy function.
The variance Ncoefs is very important, it controls the
complexity of the linear combinations. If it is too big the
linear combinations themselves can be extremely oscillatory and
stationarity is easy to obtain. Small values of Ncoefs
results in piecewise constant functions with fewer jumps.
The Ncoefs value must take the value of
2^k - 1. If this is the case the k
is the number of scale levels present in the Haar representation
of the combining function \alpha_t, \beta_t
(excluding the scaling function coefficient, just the wavelet
coefficients from the coarsest scale).
The functions to compute the linear combination and also the
test statistic on that combination, and just to compute the
combination and return also (optionally) the combination
vectors are supplied in lctsfn and prodcomb.fn.
By default, these are just the LCTS and prodcomb
functions. However, it is possible to recode these to
look at operating on combinations that operate on portfolios.
I.e. rather than look at linear combinations of log-returns
(which if tsx and tsy were) one can look at
linear combinations of actual series (ie portfolios) and
then look for stationarity of log-returns of the portfolios.
These functions will be made available in a later package.
Value
An object of class csFSS which is a
list with the following components.
startpar |
A matrix with |
endpar |
Same dimension as |
convergence |
A vector of length |
minvar |
A vector of length |
pvals |
A vector of length |
tsx |
The |
tsy |
The |
tsxname |
The name of the |
tsyname |
The name of the |
filter.number |
The filter number that was used |
family |
The wavelet family that was used |
spec.filter.number |
The filter number that was used |
spec.family |
The wavelet family that was used |
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
LCTS, BootTOS,plotBS, prodcomb, COEFbothscale,
LCTSres, print.csFSS, summary.csFSS,
plot.csFSS
Examples
#
# Find some stationary solutions with \code{Ncoefs=3}.
#
# Note: this is a toy example
#
tsx1 <- rnorm(32) # A x time series
tsy1 <- rnorm(32) # A y time series
#
# Find costationary solutions, but only from 2 random starts
#
# Typically, the length of tsx and tsy would be bigger (eg sret, fret are
# other examples you might use). Also, Nsims would be bigger, you need
# to use many random starts to ensure good coverage of the solution
# space, e.g. Nsims=100
#
# Note: the following examples are not run so as to adhere to CRAN
# requirements for package execution timings
#
## Not run: ans <- findstysols(Nsims=3, tsx=tsx1, tsy=tsy1)
#
# Print out a summary of the results
#
## Not run: ans
#Class 'csFSS' : Stationary Solutions Object from costat:
# ~~~~~ : List with 13 components with names
# startpar endpar convergence minvar pvals tsx tsy tsxname tsyname
# filter.number family spec.filter.number spec.family
#
#
#summary(.):
#----------
#Name of X time series: tsx1
#Name of Y time series: tsy1
#Length of input series: 32
#There are 3 sets of solutions
#Each solution vector is based on 3 coefficients
#Some solutions did not converge, check convergence component for more information.
#Zero indicates successful convergence, other values mean different things and
#you should consult the help page for `optim' to discover what they mean
#For size level: 0.05
# 0 solutions appear NOT to be stationary
# 3 solutions appear to be stationary
#Range of p-values: ( 0.93 , 0.995 )
#
#Wavelet filter for combinations: 1 DaubExPhase
#Wavelet filter for spectrum: 1 DaubExPhase
#
#______________
#
# Ok. The printout above suggests that some solutions did not converge.
# Which ones?
#
## Not run: ans$convergence
# [1] 0 1 0
#
# The second one did not converge, the others did. Good. The printout
# above also indicates that all the resultant solutions were stationary
# (this is not surprising for this example, as the inputs tsx1 and tsy1
# are stationary, and indeed iid).
#
# Let's see how the solutions compare. For example, let's plot the
# hierarchical cluster analysis of the final solutions (those that
# converged and are stationary)
#
## Not run: plot(ans, ALLplotscale=FALSE)
#
# My cluster shows that solution 1 and 3 are similar. Let's
# view solution 3.
#
## Not run: oldpar <- par(mfrow=c(2,2))
## Not run: plot(ans, solno=3)
## Not run: par(oldpar)
Particular section of FTSE log-return series.
Description
Observations 256:767 from the SP500 log-returns series
stored in SP500FTSElr dataset.
Usage
data(fret)Format
A vector of 512 observations of the FTSE100 log-returns series
Details
Its just more convenient to refer to fret than to
SP500FTSElr[256:767,3].
Source
Yahoo! Finance
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
Examples
## Not run: ts.plot(fret)
Form a particular linear combination of two time series and assess the combination's stationarity p-value
Description
Given two time series, a set of combination coefficients, a function to combine them, this function makes the combination, tests the combination for stationarity, and returns the pvalue. Effectively, returns "how stationary" the combination is.
Usage
getpvals(par, prodcomb.fn, tsx, tsy, filter.number,
family=c("DaubExPhase", "DaubLeAsymm"),
verbose, tos = BootTOS, Bsims = 100, lapplyfn = lapply)
Arguments
par |
The coefficients used to make the combination via the
|
prodcomb.fn |
The function which computes the combination given the two time series and the combination parameters. |
tsx |
One of the time series. |
tsy |
The other time series. |
filter.number |
Wavelet smoothness to be used in the time series combination. |
family |
Wavelet family to be used in the time series combination. |
verbose |
Supplied directly to the call to |
tos |
The function the computes a test of stationarity |
Bsims |
Number of bootstrap simulations the test uses (if it does) |
lapplyfn |
The function used to process lists. Can be the regular
|
Value
A single number between zero and one indicating the p-value from the hypothesis test of stationarity of the combination.
Author(s)
G. P. Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# Generate two toy time series data sets
#
x1 <- rnorm(32)
y1 <- rnorm(32)
#
# Generate two toy sets of parameters (for combination)
#
tmp.a <- c(1,-1)
tmp.b <- c(0.5, 0.5)
#
# Call the function and find out the degree of stationarity of this
# combination
#
## Not run: ans <- getpvals(c(tmp.a, tmp.b), prodcomb.fn=prodcomb, tsx=x1, tsy=y1,
filter.number=1, family="DaubExPhase")
## End(Not run)
#
# What is the p-value?
#
## Not run: ans
# [1] 0.53
Computes localized (wavelet) autocovariance function
Description
Compute the LACV function for a locally stationary wavelet process.
Usage
lacv(x, filter.number = 10,
family = c("DaubExPhase", "DaubLeAsymm"), smooth.dev=var,
AutoReflect=TRUE, lag.max=NULL, smooth.RM=0, ...)
Arguments
x |
The time series you want to compute the LACV for |
filter.number |
The wavelet that you wish to compute the LACV with respect to |
family |
The wavelet family |
smooth.dev |
The deviance used in smoothing if running mean smoothing
is not used, ie in the call to |
AutoReflect |
If TRUE then the spectrum is computed on a boundary-corrected series, overcoming the lack of periodicity in the time series. |
lag.max |
The maximum lag that the function computes. If this option
is |
smooth.RM |
If this is zero then regular wavelet smoothing of the periodogram will be used. If not zero then running mean smoothing of the periodogram will be used with a bandwidth given by this argument. |
... |
Additional arguments to the spectrum computation contained within |
Details
A locally stationary wavelet process is a particular kind of non-stationary time series constructed out of wavelet atoms, with a time-varying spectrum (slowly varying). This kind of model is useful for time series whose spectral properties change over time.
The time-varying spectrum can be computed from within the
WaveThresh library by the ewspec function. However,
just as in the classical stationary case, where the
spectrum and autocovariance are a Fourier transform pair, the
paper Nason, von Sachs, Kroisandt (2000) [NvSK2000] shows that the
evolutionary wavelet spectrum is paired to a localized
autocovariance function using a wavelet-like transform.
This is expressed in formula (14) of the NvSK2000 paper.
This function computes the localized autocovariance by first computing the estimate of the evolutionary spectrum, and then directly transforming it using formula (14) via the autocorrelation wavelet transform.
Value
An object of class lacv. This is a list with the following
components: lacv which is a matrix that contains the localized
autocovariance.
If the original time series was of length T, then the number
of rows of the returned matrix is also T, one row for each time
point.
The columns of the array correspond to the lag. The number of
columns, 2K+1, depends both on the length of the time series and
also the order of the wavelet (smoother wavelets return
lacv matrices with larger number of lags). Lag 0 is always
the centre column, with negative lags from -K to -1 are
the leftmost columns, lags from 1 to K are the rightmost columns;
lacr: a matrix, with the same dimensions as lacv
but containing the local autocorrelations; date: the date
this function was executed.
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
Nason, G.P., von Sachs, R. and Kroisandt, G. (2000) Wavelet processes and adaptive estimation of the evolutionary wavelet spectrum. J. R. Statist. Soc. B, 62, 271-292.
See Also
ewspec, print.lacv, plot.lacv,
summary.lacv
Examples
#
# Generate an AR(1) time series
#
vsim <- arima.sim(model=list(ar=0.8), n=1024)
#
# Compute the ACF of this stationary series
#
vsim.acf <- acf(vsim, plot=FALSE)
#
# Compute the localized autocovariance. We'll use
# a reasonably smooth wavelet.
#
vsim.lacv <- lacv(vsim, filter.number=4, lag.max=30)
#
# Now plot the time-varying autocorrelations, only the first 5 lags
#
## Not run: plot(vsim.lacv, lags=0:5)
#
# Now plot the localized autocorrelation at time t=100, a plot similar
# to the usual R acf plot.
#
## Not run: plot(vsim.lacv, type="acf", the.time=100)
Compute the time-localized (unconditional) variance for a time series
Description
Compute the time localized variance from an evolutionary wavelet spectrum of a time series
Usage
localvar(spec)
Arguments
spec |
An evolutionary wavelet spectrum, such as that computed
by |
Details
One can compute the local variance of a time series by first
computing its evolutionary wavelet spectrum, e.g., by using
ewspec, and then applying localvar on the
S component of that returned by ewspec.
Value
A vector representing the local variance estimate at successive times.
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
ewspec
Examples
#
# Let's look at a iid standard normal sequence, variance should be 1, always
# for all times.
#
zsim <- rnorm(64)
#
# Note, in the following I use var as the method of deviance estimation,
# as described in the help there it can be more accurate when transformations
# are not used.
#
z.ews <- ewspec(zsim, smooth.dev=var)$S
#
# Compute the local variance
#
z.lv <- localvar(z.ews)
#
# Plot the local variance against time
#
## Not run: ts.plot(z.lv)
#
# Should be around 1. Note, the vertical scale of the plot might be
# deceptive, as R plots expand the function to the maximum available
# space. If you look again it should be quite close to 1 (e.g. on the
# example I am looking at now the variance is within +/- 0.15 of 1.
#
# However, it might not be close to 1 because the sample size is quite small,
# only 64, so repeat the above analysis with a larger sample size, e.g. 1024.
#
Concatenate a set of solution results into one set
Description
Merges several sets of optimization results from
multiple calls to findstysols into
a single object for further analysis
Usage
mergexy(...)
Arguments
... |
An unspecified number of arguments of class |
Details
The return object from an invocation of the
findstysols is a list containing a number
of interesting components containing information about
the starting parameters, the (hopefully optimal) ending
parameters, convergence status, minimum variance achieved
and p-value associated with the final test of stationarity
after an optimization.
It is possible to ask findstysols to execute
multiple optimization runs in the same function, by choice of
the Nsims parameter. However, for truly large runs,
it can be convenient to run multiple copies of
findstysols, for example on multiple processors
simultaneously (a coarse grained parallelism).
In particular, for large time series, it can be useful to run
findstysols for one optimization run
(as running more than one for a very large series can cause the
software to fail as R can run out of memory. Actually, for very
very large series even one optmization run can fail for memory
reasons).
In this way multiple optimization runs can be executed with each
one producing its own set of results. This function
(mergexy) takes a list of object names of all of the results,
and merges the results into one object as if a single call
to findstysols had been executed. Such a single
set of results can then be passed on to further analysis
routines, such as COEFbothscale or
LCTSres.
Value
A set of optimization solutions in the same format as
those returned by findstysols
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
findstysols, LCTSres,
COEFbothscale
Examples
#
# Generate two dummy time series
#
x1 <- rnorm(32)
y1 <- rnorm(32)
#
# Run two optimizations
#
## Not run: solnset1 <- findstysols(Nsims=1, tsx=x1, tsy=y1)
## Not run: solnset2 <- findstysols(Nsims=1, tsx=x1, tsy=y1)
#
# Merge them
#
## Not run: solnset <- mergexy(solnset1, solnset2)
Plots results of a Bootstrap Test of Stationarity
Description
Produces Bootstrap simulation result as a histogram with a vertical line indicating the test statistic computed on the actual data.
Usage
## S3 method for class 'BootTOS'
plot(x, ...)
Arguments
x |
The object you wish to get a plot on. |
... |
Other arguments to plot. |
Details
Produces a histogram of all the bootstrap statistics and the test statistic computed on the true data. Also produces a vertical line indicating the position of the true statistic.
Value
None.
Author(s)
G.P. Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1. Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
v <- rnorm(512)
## Not run: v.BootTOS <- BootTOS(v)
## Not run: plot(v.BootTOS)
Plot a csBiFunction object
Description
A csBiFunction object contains representations of
two functions. This function plots the two functions superimposed.
Usage
## S3 method for class 'csBiFunction'
plot(x, ...)
Arguments
x |
An object of class |
... |
Other arguments to plot call |
Value
None
Author(s)
G.P. Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
coeftofn, print.csBiFunction,
summary.csBiFunction
Examples
## Not run: plot(coeftofn(c(1,-1), c(0.5, 0.5)))
Plot a csFSS object.
Description
Produces two types of plot from the information in
a csFSS object, such as that returned by
findstysols.
Usage
## S3 method for class 'csFSS'
plot(x, solno = NULL, ALLplotclust = TRUE, ALLplotscale = TRUE, sollabels=TRUE,
SNinc = 0, ...)
Arguments
x |
The |
solno |
If missing then the plot produces plots that show information on all solutions at once, first in a scatter plot, then in a dendrogram. If provided then the plot produces information on that specific solution. |
ALLplotclust |
If TRUE then the dendrogram is plotted, if FALSE it is not. |
ALLplotscale |
If TRUE then the two-dimensional scaling solution is plotted. If FALSE, it is not. |
sollabels |
If TRUE then solution numbers are plotted on the scaling plot, if produced. |
SNinc |
An argument passed to the |
... |
Other arguments passed to plot. |
Details
This function can produce either a scatterplot, which indicates
the two-dimensional scaling picture of the optimization solution
sets, or a dendrogram showing putative clustering of solutions.
In both cases it is a plot considering ALL solutions at once.
These plots are delegated to the plot.csFSSgr
function.
If the argument solno is provided then plots are produced
which show information on a single solution. This plot is
delegated to the LCTSres function.
Value
None.
Author(s)
G.P.Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
findstysols,
LCTSres,
plot.csFSSgr, print.csFSS,
summary.csFSS
Examples
#
# Create dummy data
#
x1 <- rnorm(32)
y1 <- rnorm(32)
#
# Find stationary combinations
# Note: we don't run this example in installation/package formation as
# it takes a long time. However, this precise command IS run in
# the help to findstysols
#
## Not run: ans <- findstysols(Nsims=100, tsx=x1, tsy=y1)
#
# Produce dendrogram
#
## Not run: plot(ans)
#
# Produce four pictures relating to solution 3 (can also do
# par(mfrow=c(2,2)) to make a nice 4 plot on one page.)
#
## Not run: plot(ans, solno=3)
#solno is 3
#3
#1:
Produce plots from a csFSSgr object.
Description
A csFSS object contains a set of solutions obtained
from a series of optimizations. Each solution corresponds to
a time-varying linear combination of two time series (or
rather the wavelet coefficients of such combinations) where
the combination has found to be stationary and the optimizer that
got there converged. Often one wishes to interrogate the results,
such as seeing how the solutions cluster, or what their low-dimensional
scaling solution projection looks like, such analyses are produced
by the COEFbothscale function and the whole
plot is marshalled by the plot.csFSS function.
Usage
## S3 method for class 'csFSSgr'
plot(x, plotclust = TRUE, plotscale = TRUE, sollabels=FALSE, ...)
Arguments
x |
The |
plotclust |
If TRUE then the dendrogram clustering is plotted, if FALSE it is not. |
plotscale |
If TRUE then the scaling solution picture is plotted, if FALSE it is not. |
sollabels |
If TRUE then solution numbers are plotted on the scaling plot, if produced. |
... |
Other arguments to plot. |
Value
None.
Author(s)
G.P. Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# This function is a helper function for plot.csFSS so see the example there.
#
Plot localized autocovariance (lacv) object.
Description
Produces various ways of looking at a localized autocovariance (lacv) object.
Usage
## S3 method for class 'lacv'
plot(x, plotcor = TRUE, type = "line",
lags = 0:min(as.integer(10 * log10(nrow(x$lacv))), ncol(x$lacv) - 1),
tcex = 1, lcol = 1, llty = 1, the.time = NULL, ...)
Arguments
x |
The localized autocovariance object you want to plot (lacv) |
plotcor |
If TRUE then plot autocorrelations, otherwise plot autocovariances. |
type |
The lacv objects are fairly complex and so there are
different ways you can plot them. The |
lags |
The |
tcex |
In the |
lcol |
Controls the colours of the lines in the |
llty |
Controls the line types of the lines in the |
the.time |
If the |
... |
Other arguments to plot. |
Details
This function produces pictures of the
two-dimensional time-varying autocovariance
or autocorrelation, c(t, \tau),
of a locally stationary time series.
There are three types of plot depending on the argument to
the type argument.
The line plot draws the autocorrelations as a series of
lines, one for each lag, as lines over time. E.g. a sequence
#of lines c(t, \tau_i) is drawn, one for each \tau_i.
The zeroth lag line is the autocorrelation at lag 0 which is
always 1. By default all the lags are drawn which can result
in a confusing picture. Often, one is only interested in the low
level lags, so only these can be plotted by changing the lags
argument and any selection of lags can be plotted. The colour
and line type of the plotted lines can be changed with the
lcol and the llty arguments.
The acf plot produces pictures similar to the standard
R acf() function plot. However, the regular acf is a
1D function, since it is defined to be constant over all time.
The time-varying acf supplied to this function is not constant
over all time (except for stationary processes, theoretically).
So, this type of plot requires the user to specify a fixed
time at which to produce the plot, and this is supplied by
the the.time argument.
The persp plot plots the 2D function c(t, \tau)
as a perspective plot.
Value
For the acf type plot the acf values are returned
invisibly. For the other types nothing is returned.
Author(s)
G.P. Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# Make some dummy data, e.g. white noise
#
v <- rnorm(256)
#
# Compute the localized autocovariance (ok, the input is stationary
# but this is just an example. More interesting things could be achieved
# by putting the results of simulating from a LSW process, or piecewise
# stationary by concatenating different stationary realizations, etc.
#
vlacv <- lacv(v, lag.max=30)
#
# Now let's do some plotting of the localized autocovariance
#
## Not run: plot(vlacv, lags=0:6)
#
# Should get a plot where lag 0 is all up at value 1, and all other
# autocorrelations are near zero (since its white noise).
#
#
# How about just looking at lags 0, 2 and 4, and some different colours.
#
## Not run: plot(vlacv, lags=c(0,2,4), lcol=c(1,2,3))
#
# O.k. Let's concentrate on time t=200, let's look at a standard acf
# plot near there.
#
## Not run: plot(vlacv, type="acf", the.time=200)
#
# Now plot the autocovariance, rather than the autocorrelation.
#
## Not run: plot(vlacv, type="acf", the.time=200, plotcor=FALSE)
#
# Actually, the plot doesn't look a lot different as the series is white
# noise, but it is different if you look closely.
Compute p-value for parametric Monte Carlo test and optionally plot test statistic values
Description
Computes and returns a p-value for the result of a parametric Monte Carlo test. Optionally, plots a histogram of the test statistics (on the original data, and using test statistics resulting from simulations from the null hypothesis distribution).
Usage
plotBS(BS, alpha = 0.05, plot = TRUE, verbose = FALSE, main = "Bootstrap Histogram",
xlab = "Test Statistic Values", ylab = "Frequency")
Arguments
BS |
The results from a Monte Carlo test. This should be a vector of arbitrary length. The first value must be the value of the test statistic computed on the data. The remaining values are the test statistics computed on simulations constructed under the null hypothesis. |
alpha |
A nominal size for the test. This only effects the reporting.
If the computed p-value is less than |
plot |
If |
verbose |
If |
main |
A |
xlab |
An |
ylab |
An |
Value
The p-value computed from the Monte Carlo test results is returned
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# See example in \code{\link{BootTOS}}.
#
Print a csBiFunction object.
Description
A csBiFunction object contains representations of
two functions. This function prints information about the object
Usage
## S3 method for class 'csBiFunction'
print(x, ...)
Arguments
x |
The object you want printed. |
... |
Other arguments |
Value
None
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
plot.csBiFunction, summary.csBiFunction
Examples
print(coeftofn(c(1,-1), c(0.5, 0.5)))
#Class 'csBiFunction' : Contains two sampled functions:
# ~~~~ : List with 2 components with names
# alpha beta
#
#
#summary(.):
#----------
#Length of functions is: 256
Print acsFSS object.
Description
Print information about a csFSS object.
Usage
## S3 method for class 'csFSS'
print(x, ...)
Arguments
x |
The |
... |
Other arguments. |
Value
None
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
findstysols, plot.csFSS,
summary.csFSS
Examples
#
# Create dummy data
#
x1 <- rnorm(32)
y1 <- rnorm(32)
#
# Find stationary combinations. Note: normally Nsims would be much bigger
#
## Not run: ans <- findstysols(Nsims=100, tsx=x1, tsy=y1)
#
# Print this csFSS object
#
## Not run: print(ans)
#Class 'csFSS' : Stationary Solutions Object from costat:
# ~~~~~ : List with 13 components with names
# startpar endpar convergence minvar pvals tsx tsy tsxname tsyname filter.number
# family spec.filter.number spec.family
#
#
#summary(.):
#----------
#Name of X time series: x1
#Name of Y time series: y1
#Length of input series: 32
#There are 100 sets of solutions
#Each solution vector is based on 3 coefficients
#Some solutions did not converge, check convergence component for more information.
#Zero indicates successful convergence, other values mean different things and
#you should consult the help page for `optim' to discover what they mean
#For size level: 0.05
# 0 solutions appear NOT to be stationary
# 97 solutions appear to be stationary
#Range of p-values: ( 0.885 , 0.975 )
#
#Wavelet filter for combinations: 1 DaubExPhase
#Wavelet filter for spectrum: 1 DaubExPhase
Print csFSSgr object.
Description
Prints out information on a csFSSgr object.
Usage
## S3 method for class 'csFSSgr'
print(x, ...)
Arguments
x |
The |
... |
Other arguments. |
Value
None
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# The user should normally never need to use this function as the
# csFSSgr object is only ever internally produced and used.
#
Print lacv class object
Description
Prints information about lacv class object.
Usage
## S3 method for class 'lacv'
print(x, ...)
Arguments
x |
The lacv class object you want to print |
... |
Other arguments |
Value
None
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# Make some dummy data, e.g. white noise
#
v <- rnorm(256)
#
# Compute the localized autocovariance (ok, the input is stationary
# but this is just an example. More interesting things could be achieved
# by putting the results of simulating from a LSW process, or piecewise
# stationary by concatenating different stationary realizations, etc.
#
vlacv <- lacv(v, lag.max=30)
#
# Now let's print the lacv object
#
print(vlacv)
#Class 'lacv' : Localized Autocovariance/correlation Object:
# ~~~~ : List with 3 components with names
# lacv lacr date
#
#
#summary(.):
#----------
#Name of originating time series:
#Date produced: Thu Oct 25 12:11:29 2012
#Number of times: 256
#Number of lags: 30
Combine two time series using a time-varying linear combination.
Description
This function takes the cfs vector and splits it
into two halves. The first half contains the wavelet coefficients
for the alpha linear combination function, and the second
half for the beta one. Then the functions themselves are
generated by using the coeftofn function. Then, the
coefficient functions are multiplied by the respective time
series (tsx by alpha and tsy by beta)
and the result returned.
Usage
prodcomb(cfs, tsx, tsy, filter.number = 1,
family = c("DaubExPhase", "DaubLeAsymm"), all = FALSE)
Arguments
cfs |
Wavelet coefficients of the two combination functions. The coefficients for alpha/beta combination functions are stored in the first/last half of the vector. |
tsx |
The x time series to combine |
tsy |
The y time series to combine |
filter.number |
The wavelet filter to use to obtain functions from coefficients |
family |
The wavelet family to do the same. |
all |
If TRUE then a list containing the combined series
in the component |
Details
This function is called by findstysols and makes
use of coeftofn to turn coefficients into a
function used in the combination.
Value
If all=TRUE then a list with the following components:
lcts |
The combined series, |
alpha |
The |
beta |
The |
If all=FALSE then only lcts is returned.
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# Toy example
#
tmp.a <- c(1, -1)
tmp.b <- c(0.5, 0.5)
#
# Generate toy time series
#
xxx <- rnorm(256)
yyy <- rnorm(256)
#
# Combine xxx and yyy using the functions produced by inverse wavelet
# transform of tmp.a and tmp.b
#
## Not run: tmp <- prodcomb(c(tmp.a, tmp.b), tsx=xxx, tsy=yyy)
#
# E.g. plot combination
#
## Not run: ts.plot(tmp)
#
# Potentially test its stationarity.... etc
#
Particular section of SP500 log-returns series.
Description
Observations 256:767 from the SP500 log-return series
stored in SP500FTSElr dataset.
Usage
data(sret)Format
A vector of 512 observations of the SP500 log-returns series.
Details
Its just more convenient to refer to sret than to
SP500FTSElr[256:767,2].
Source
Yahoo! Finance
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
Examples
## Not run: ts.plot(sret)
Summarize a csBiFunction object.
Description
Summarize a csBiFunction object.
Usage
## S3 method for class 'csBiFunction'
summary(object, ...)
Arguments
object |
The object to summarize |
... |
Other arguments |
Value
None
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
plot.csBiFunction, print.csBiFunction
Examples
#
# See example to print.csBiFunction, as this calls summary(.)
#
Summarize a csFSS object.
Description
Summarizes a csFSS object.
Usage
## S3 method for class 'csFSS'
summary(object, size = 0.05, ...)
Arguments
object |
Object you wish to summarize. |
size |
A hypothesis test size. The |
... |
Other arguments |
Value
None
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
findstysols,plot.csFSS, print.csFSS
Examples
#
# See example to print.csFSS which calls summary(.)
#
Summarize a csFSSgr object.
Description
Summarizes a csFSSgr object.
Usage
## S3 method for class 'csFSSgr'
summary(object, ...)
Arguments
object |
The |
... |
Other arguments |
Value
None
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# See example for print.csFSSgr which calls summary(.)
Summarizes a lacv object
Description
Summarizes a lacv object
Usage
## S3 method for class 'lacv'
summary(object, ...)
Arguments
object |
The lacv object you wish summarized. |
... |
Other arguments |
Value
None
Author(s)
Guy Nason
References
Cardinali, A. and Nason, Guy P. (2013) Costationarity of Locally Stationary Time Series Using costat. Journal of Statistical Software, 55, Issue 1.
Cardinali, A. and Nason, G.P. (2010) Costationarity of locally stationary time series. J. Time Series Econometrics, 2, Issue 2, Article 1.
See Also
Examples
#
# Make some dummy data, e.g. white noise
#
v <- rnorm(256)
#
# Compute the localized autocovariance (ok, the input is stationary
# but this is just an example. More interesting things could be achieved
# by putting the results of simulating from a LSW process, or piecewise
# stationary by concatenating different stationary realizations, etc.
#
vlacv <- lacv(v, lag.max=20)
#
# Now let's summarize the lacv object
#
summary(vlacv)
#Name of originating time series:
#Date produced: Thu Oct 25 12:11:29 2012
#Number of times: 256
#Number of lags: 20