# ArithmeticConstantModel

class sherpa.models.model.ArithmeticConstantModel(val: , name: = None)[source] [edit on github]

Bases: Model

Represent a constant value, or values.

Parameters:
• val (number or sequence) – The number, or numbers, to store.

• name (str or None, optional) – The display name. If not set the value is used when the value is a scalar, otherwise it indicates an array of elements.

Attributes Summary

 lpars Return any linked parameters. ndim The dimensionality of the model, if defined, or None. pars Return the parameters of the model. thawedparhardmaxes The hard maximum values for the thawed parameters. thawedparhardmins The hard minimum values for the thawed parameters. thawedparmaxes The maximum limits of the thawed parameters. thawedparmins The minimum limits of the thawed parameters. thawedpars The thawed parameters of the model. val The constant value (scalar or 1D).

Methods Summary

 calc(p, *args, **kwargs) Evaluate the model on a grid. freeze() Freeze any thawed parameters of the model. Return the thawed parameter objects. guess(dep, *args, **kwargs) Set an initial guess for the parameter values. reset() Reset the parameter values. set_center(*args, **kwargs) startup([cache]) Called before a model may be evaluated multiple times. teardown() Called after a model may be evaluated multiple times. thaw() Thaw any frozen parameters of the model.

Attributes Documentation

lpars

This only returns linked parameters that are not related to the model, and each parameter is not repeated.

pars

Examples

By default there are no linked parameters:

>>> from sherpa.models.basic import Gauss2D
>>> mdl = Gauss2D("mdl")
>>> len(mdl.pars)
6
>>> mdl.lpars
()

Force the model to have identical xpos and ypos parameters. Since the linked parameter value (mdl.xpos) is part of the model it is not included in lpars:

>>> mdl.ypos = mdl.xpos
>>> len(mdl.pars)
6
>>> mdl.lpars
()

Add a link to allow the sigma term to be fit rather than FWHM. Since the linked parameter - here from the Const1D model - is not a part of the model it is included in lpars:

>>> import numpy as np
>>> from sherpa.models.basic import Const1D
>>> sigma = Const1D("sigma")
>>> mdl.fwhm = 2 * np.sqrt(2 * np.log(2)) * sigma.c0
>>> len(mdl.pars)
6
>>> mdl.lpars
(<Parameter 'c0' of model 'sigma'>,)
ndim: int | None = None

The dimensionality of the model, if defined, or None.

pars

Return the parameters of the model.

This does not include any linked parameters.

Changed in version 4.16.1: The pars field can no-longer be set directly. Individual elements can still be changed.

lpars

thawedparhardmaxes

The hard maximum values for the thawed parameters.

The minimum and maximum range of the parameters can be changed with thawedparmins and thawedparmaxes but only within the range given by thawedparhardmins to thawparhardmaxes.

thawedparhardmins

The hard minimum values for the thawed parameters.

The minimum and maximum range of the parameters can be changed with thawedparmins and thawedparmaxes but only within the range given by thawedparhardmins to thawparhardmaxes.

thawedparmaxes

The maximum limits of the thawed parameters.

Get or set the maximum limits of the thawed parameters of the model as a list of numbers. If there are no thawed parameters then [] is used. The ordering matches that of the pars attribute.

thawedpars, thawedarhardmaxes, thawedparmins

thawedparmins

The minimum limits of the thawed parameters.

Get or set the minimum limits of the thawed parameters of the model as a list of numbers. If there are no thawed parameters then [] is used. The ordering matches that of the pars attribute.

thawedpars, thawedarhardmins, thawedparmaxes

thawedpars

The thawed parameters of the model.

Get or set the thawed parameters of the model as a list of numbers. If there are no thawed parameters then [] is used. The ordering matches that of the pars attribute.

val

The constant value (scalar or 1D).

Methods Documentation

calc(p, *args, **kwargs)[source] [edit on github]

Evaluate the model on a grid.

Parameters:
• p (sequence of numbers) – The parameter values to use. The order matches the pars field.

• *args – The model grid. The values can be scalar or arrays, and the number depends on the dimensionality of the model and whether it is being evaluated over an integrated grid or at a point (or points).

• **kwargs – Any model-specific values that are not parameters.

freeze() None [edit on github]

Freeze any thawed parameters of the model.

get_center() [edit on github]
get_thawed_pars()  [edit on github]

Return the thawed parameter objects.

This includes linked parameters, which complicates the min/max settings, since the range on the components of a linked parameter does not match that of the original parameter, which is an issue when the limits are exceeded.

guess(dep, *args, **kwargs) [edit on github]

Set an initial guess for the parameter values.

Attempt to set the parameter values, and ranges, for the model to match the data values. This is intended as a rough guess, so it is expected that the model is only evaluated a small number of times, if at all.

reset() None [edit on github]

Reset the parameter values.

Restores each parameter to the last value it was set to. This allows the parameters to be easily reset after a fit.

set_center(*args, **kwargs) [edit on github]
startup(cache: bool = False) None[source] [edit on github]

Called before a model may be evaluated multiple times.

Parameters:

cache (bool, optional) – Should a cache be used when evaluating the models.

teardown

teardown() None[source] [edit on github]

Called after a model may be evaluated multiple times.