Last modified: December 2020

URL: https://cxc.cfa.harvard.edu/sherpa/ahelp/freeze.html
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AHELP for CIAO 4.13 Sherpa v1

freeze

Context: modeling

Synopsis

Fix model parameters so they are not changed by a fit.

Syntax

freeze(*args)

Description

If called with no arguments, then all parameters of models in source expressions are frozen. The arguments can be parameters or models (in which case all parameters of the model are frozen).


Examples

Example 1

Fix the FWHM parameter of the line model (in this case a `gauss1d` model) so that it will not be varied in the fit.

>>> set_source(const1d.bgnd + gauss1d.line)
>>> line.fwhm = 2.1
>>> freeze(line.fwhm)
>>> fit()

Example 2

Freeze all parameters of the line model and then re-fit:

>>> freeze(line)
>>> fit()

Example 3

Freeze the nh parameter of the gal model and the abund parameter of the src model:

>>> freeze(gal.nh, src.abund)

Notes

The `thaw` function can be used to reverse this setting, so that parameters can be varied in a fit.


Bugs

See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.

See Also

contrib
renorm
fitting
fit
modeling
guess, link, paramprompt, set_par, thaw, unlink