Do not allow indicated model parameters to vary. (See also thaw.)
XSPEC> freeze [<model parameter range>...]
where <model parameter range> =:: <model parameter no.> OR
<model param no.>-<model param no.>.
The indicated model parameter or range of model parameters will be marked
so they cannot be varied by the fit command by setting their associated
<delta> to less than zero (see newpar command). By default,
the range will be the last range input by either a freeze or thaw
command.