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Last modified: December 2013

URL: http://cxc.harvard.edu/sherpa/ahelp/guess.html
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AHELP for CIAO 4.9 Sherpa v1

guess

Context: modeling

Synopsis

Estimate initial parameter values and ranges

Syntax

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

Description

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.

  • id - the id of the dataset; if not given, uses the default dataset id (id=1 by default, see "ahelp get_default_id")
  • model - initialize the values of this model component
  • limits - guess the parameter limits? True (default)=yes, False=no
  • values - guess the initial parameter values? True (default)=yes, False=no

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
powlaw1d.p1
   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".

Bugs

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

See Also

contrib
renorm
modeling
freeze, link, paramprompt, set_par, thaw, unlink

Last modified: December 2013
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