link

Context: modeling

Synopsis

Link a parameter to a value.

Syntax

link(par, val)

Description

A parameter can be linked to another parameter value, or function of that value, rather than be an independent value. As the linked-to values change, the parameter value will change.

Examples

Example 1

The fwhm parameter of the g2 model is set to be the same as the fwhm parameter of the g1 model.

>>> link(g2.fwhm, g1.fwhm)

Example 2

Fix the pos parameter of g2 to be 2.3 more than the pos parameter of the g1 model.

>>> gauss1d.g1
>>> gauss1d.g2
>>> g1.pos = 12.2
>>> link(g2.pos, g1.pos + 2.3)
>>> g2.pos.val
14.5
>>> g1.pos = 12.1
>>> g2.pos.val
14.399999999999999

PARAMETERS

The parameters for this function are:

Parameter	Type information	Definition
par	str or Parameter	The parameter to link.
val		The value - which can be a numeric value or a function of other model parameters, to set `par` to.

Notes

The link attribute of the parameter is set to match the mathematical expression used for `val` .

In the following, the fit will vary the pos parameter even though the src2 component is not part of the source expression (this behavior changed in the 4.16.1 release):

>>> set_source(1, gauss1d.src1)
>>> gauss1d.src2
>>> link(src1.pos, src2.pos)
>>> fit(1)

The lpars attribute of a source model will include these "extra" parameters:

>>> get_source(1).lpars
(<Parameter 'pos' of model 'src2'>,)

Changes in CIAO

Changed in CIAO 4.17

Source models no longer have to contain the linked parameter.

Bugs

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