Last modified: December 2013

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AHELP for CIAO 4.12 Sherpa v1


Context: modeling


Estimate initial parameter values and ranges


guess([id], model, [limits=True,] [values=True])


The guess command estimates initial parameter values and the minimum and maximum range values based on the input data. For spectral fitting, an appropriate response should be defined before running guess.

By default, both the parameter values and the limits are guessed. This can be restricted to one or the other by changing the "limits" or "values" option.


Example 1

sherpa> set_source("src", powlaw1d.p1)
sherpa> guess("src", p1)

Set a model for the dataset "src", then guess the initial parameter values of p1.

sherpa> show_source("src")
Model: src
   Param        Type          Value          Min          Max      Units
   -----        ----          -----          ---          ---      -----
   p1.gamma     thawed            1          -10           10
   p1.ref       frozen            1 -3.40282e+38  3.40282e+38
   p1.ampl      thawed  0.000150152  1.50152e-06    0.0150152

Example 2

sherpa> set_source(powlaw1d.p1 * gauss1d.g1)
sherpa> guess(p1)
sherpa> guess(g1)

Establish a model for the default dataset, then run guess on each component separately.

Example 3

sherpa> set_source(powlaw1d.p1 * gauss1d.g1)
sherpa> guess(p1, limits=False)
sherpa> guess(g1, values=False)

Set the source model for the default dataset. Guess is run to determine the values of the model component "p1" and the limits of the model component "g1".


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

See Also

freeze, link, paramprompt, set_par, thaw, unlink