Last modified: December 2018

URL: http://cxc.harvard.edu/sherpa/ahelp/lorentz2d.html
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AHELP for CIAO 4.11 Sherpa v1

lorentz2d

Context: models

Synopsis

Two-dimensional un-normalised Lorentz function.

Syntax

lorentz2d

Example

>>> create_model_component("lorentz2d", "mdl")
>>> print(mdl)

Create a component of the lorentz2d model and display its default parameters. The output is:

mdl
   Param        Type          Value          Min          Max      Units
   -----        ----          -----          ---          ---      -----
   mdl.fwhm     thawed           10  1.17549e-38  3.40282e+38           
   mdl.xpos     thawed            0 -3.40282e+38  3.40282e+38           
   mdl.ypos     thawed            0 -3.40282e+38  3.40282e+38           
   mdl.ellip    frozen            0            0        0.999           
   mdl.theta    frozen            0     -6.28319      6.28319    radians
   mdl.ampl     thawed            1 -3.40282e+38  3.40282e+38           

ATTRIBUTES

The attributes for this object are:

fwhm

The full-width half maximum.

xpos

The center of the model on the x0 axis.

ypos

The center of the model on the x1 axis.

ellip

The ellipticity of the model.

theta

The angle of the major axis. It is in radians, measured counter-clockwise from the X0 axis (i.e. the line X1=0).

ampl

The amplitude refers to the maximum peak of the model.

Notes

The functional form of the model for points is:

f(x0,x1) = ampl / (1 + 4 * r(x0,x1)^2)

r(x0,x1)^2 = xoff(x0,x1)^2 * (1-ellip)^2 + yoff(x0,x1)^2
             -------------------------------------------
                         fwhm^2 * (1-ellip)^2

xoff(x0,x1) = (x0 - xpos) * cos(theta) + (x1 - ypos) * sin(theta)

yoff(x0,x1) = (x1 - ypos) * cos(theta) - (x0 - xpos) * sin(theta)

and for an integrated grid it is the integral of this over the bin.


Bugs

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

See Also

models
devaucouleurs2d, hubblereynolds, sersic2d