expTransform {tigre} | R Documentation

## Constrains a parameter.

### Description

contains commands to constrain parameters to be positive via exponentiation or within a fixed interval via the sigmoid function.

### Usage

    expTransform(x, transform)
    sigmoidTransform(x, transform)
    boundedTransform(x, transform, bounds)

### Arguments

`x` | input argument.
`transform` | type of transform, 'atox' maps a value into the transformed space (i.e. makes it positive). 'xtoa' maps the parameter back from transformed space to the original space. 'gradfact' gives the factor needed to correct gradients with respect to the transformed parameter.
`bounds` | a 2-vector of bounds of allowed values in boundedTransform

### Value

Return value as selected by `tranform`

### See Also

`modelOptimise`

### Examples

      # Transform unconstrained parameter -4 to a positive value
      expTransform(-4, 'atox')

      # Transform a bounded parameter in (1,3) to an unconstrained one
      boundedTransform(2, 'xtoa', c(1, 3))

[Package tigre version 1.40.0 Index]