# Variable Types

Table 59 shows the different type of script variables that are available in the verbatim sections of PoPy scripts:-

Table 59 PoPy Variable Types
Type | Description | Defined | Used
--- | --- | --- | ---
`c[X]` | covariates (fit) | data file/PREPROCESS | main sections
`c[X]` | covariates (gen) | EFFECTS | main sections
`c[X]` | observations | PREDICTIONS (fit) | PREDICTIONS (gen)
`f[X]` | fixed effects | EFFECTS | MODEL_PARAMS
`r[X]` | random effects | EFFECTS | MODEL_PARAMS
`m[X]` | Model parameters | MODEL_PARAMS | main sections
`w[X]` | Workspace Variables | MODEL_PARAMS | MODEL_PARAMS
`x[NEWIND]` | First row for individual | N/A | MODEL_PARAMS
`d[X]` | Derivatives wrt time | DERIVATIVES | N/A
`s[X]` | States | DERIVATIVES/STATES | DERIVATIVES/PREDICTIONS
`x[TIME]` | Continuous time | N/A | DERIVATIVES
`p[X]` | Predictions | PREDICTIONS | PREDICTIONS

In Table 59, the ‘Defined’ column shows where a variable of particular type is first declared, typically on the left hand side of an ‘=’ or ‘~’ operator. The ‘Used’ column shows where a variable may be used, typically on the right hand side of an ‘=’ or ‘~’ operator.

Note the entry ‘main sections’ in table Table 59 above means the following sections - MODEL_PARAMS/STATES/DERIVATIVES/PREDICTIONS.