thaw: allow fixed parameters to vary.

Allow indicated parameters to vary. (See also freeze).

Syntax:           thaw{[ <param range>...]}

where

<param range> =:: [modelName:] <param #> | <param #>-- <param #>

The indicated parameter, or range of parameters, will be marked as variable by the fitting commands and treated as a fitting parameter in subsequent fits.(Note that parameters with <delta> values equal to zero are not affected. The newpar command must be used to change these.) By default, the range will be the last range input by either a freeze or thaw command. See the freeze examples for an example of the use of the thaw command.