Last modified: December 2020

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AHELP for CIAO 4.13 Sherpa v1


Context: models


Gaussian function for modeling absorption (optical depth).




This model is intended to be used to modify another model (e.g. by multiplying the two together). It is for use when the independent axis is in Angstroms.


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

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

   Param        Type          Value          Min          Max      Units
   -----        ----          -----          ---          ---      -----
   mdl.fwhm     thawed          100  1.17549e-38  3.40282e+38       km/s
   mdl.pos      frozen         5000  1.17549e-38  3.40282e+38  angstroms
   mdl.tau      thawed          0.5 -3.40282e+38  3.40282e+38           


The attributes for this object are:

Attribute Definition
fwhm The full-width half-maximum of the model in km/s.
pos The center of the gaussian, in Angstroms.
tau The optical depth of the model.
limit The model is only evaluated for points that lie within limit sigma of pos. It is a hidden parameter, with a value fixed at 4.


The functional form of the model for points is:

f(x) = exp(-tau * g(x))

g(x) = exp(-0.5 * ((x - pos) / sigma)^2)

sigma = pos * fwhm / (2.9979e5 * 2.354820044)

and for integrated data sets the low-edge of the grid is used. The calculation is only done for those points that are in the range:

|x - pos| < limit * sigma

Outside this range the model is set to 1.


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

See Also

absorptionedge, absorptiongaussian, absorptionlorentz