sherpa.astro.ui.set_par(par, val=None, min=None, max=None, frozen=None)

Set the value, limits, or behavior of a model parameter.

  • par (str) – The name of the parameter, using the format “componentname.parametername”.

  • val (number, optional) – Change the current value of the parameter.

  • min (number, optional) – Change the minimum value of the parameter (the soft limit).

  • max (number, optional) – Change the maximum value of the parameter (the soft limit).

  • frozen (bool, optional) – Freeze (True) or thaw (False) the parameter.


sherpa.utils.err.ArgumentErr – If the par argument is invalid: the model component does not exist or the given model has no parameter with that name.

See also


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


Return a parameter of a model component.


Link a parameter value to an associated value.


Allow model parameters to be varied during a fit.


Unlink a parameter value.


The parameter object can be used to change these values directly, by setting the attribute with the same name as the argument - so that:

set_par('emis.flag', val=2, frozen=True)

is the same as:

emis.flag.val = 2
emis.flag.frozen = True


Change the parameter value to 23.

>>> set_par('bgnd.c0', 23)

Restrict the line.ampl parameter to be between 1e-4 and 10 and to have a value of 0.1.

>>> set_par('line.ampl', 0.1, min=1e-4, max=10)