# Nowcasting nomenclature

Throughout this package, we will refer to different nowcasting object lists, matrices, and vectors using the following table. In this table, “point” refers to a point estimate. When not indicated, we are referring to a probabilistic draw from an observation model.

Data Structure | Observations Only | Mixed (Obs + Predictions) | Pure Predictions Only
--- | --- | --- | ---
Matrix Format | `reporting_matrix` (complete with observations) `reporting_triangle` (contains NAs for missing observations) | `point_nowcast_matrix` `nowcast_matrix` | `point_pred_matrix` `pred_matrix` (contains NAs in elements where there were observations)
List Format (multiple matrices) | `reporting_matrices` (complete) `reporting_triangles` (contains NAs for missing observations) | `nowcast_matrices` | `pred_matrices`
Vector Format (summed across delays) | `observed_cases` | `point_nowcast` `nowcast` | `point_pred` `pred`
DataFrame Format | - | `nowcast_df` | `pred_df`

For example, we refer to the matrix with imputed point estimates for all \(t+d>t^*\) as a point nowcast matrix, a matrix with a complete set of observations for all elements as a reporting matrix, and a matrix with only the predictions as a point prediction matrix.

In package documentation, we will generally use a reporting triangle to refer to a diagonal reporting triangle, which is the special case of a reporting triangle where the reporting delays and reference times are indexed on the same scale. An example of a diagonal reporting triangle is one with daily reporting of daily data. The package also supports what we refer to as a ragged reporting triangle, an example of which would be daily reporting of data referenced only once per week.

We will use the following to abbreviations to shorten names in the code when necessary:

Long Name | Code Abbreviation
--- | ---
truncated | `trunc`
retrospective | `retro`
observed | `obs`
predicted | `pred`
matrix | `mat`
point | `pt`
error | `err`