Last modified: December 2018

URL: http://cxc.harvard.edu/sherpa/ahelp/logparabola.html
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AHELP for CIAO 4.11 Sherpa v1

logparabola

Context: models

Synopsis

One-dimensional log-parabolic function.

Syntax

logparabola

Example

>>> create_model_component("logparabola", "mdl")
>>> print(mdl)

Create a component of the logparabola model and display its default parameters. The output is:

mdl
   Param        Type          Value          Min          Max      Units
   -----        ----          -----          ---          ---      -----
   mdl.ref      frozen            1 -3.40282e+38  3.40282e+38           
   mdl.c1       thawed            1 -3.40282e+38  3.40282e+38           
   mdl.c2       thawed            1 -3.40282e+38  3.40282e+38           
   mdl.ampl     thawed            1            0  3.40282e+38           

ATTRIBUTES

The attributes for this object are:

ref

The reference point for the normalization.

c1

The power-law index (gamma).

c2

The curvature of the parabola (beta).

ampl

The amplitude of the model.

Notes

The functional form of the model for points is:

f(x) = ampl * (x / ref) ^ (-c1 - c2 * log_10 (x / ref))

The grid version is evaluated by numerically intgerating the function over each bin using a non-adaptive Gauss-Kronrod scheme suited for smooth functions [1] , falling over to a simple trapezoid scheme if this fails.

References


Bugs

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

See Also

models
exp, exp10, log, log10, sqrt