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AHELP for CIAO 4.11 Sherpa v1

# gauss2d

Context: models

## Synopsis

Two-dimensional gaussian function.

## Syntax

`gauss2d`

## Example

```>>> create_model_component("gauss2d", "mdl")
>>> print(mdl)```

Create a component of the gauss2d 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 of the gaussian along the major axis. It is related to the sigma value by: FWHM = sqrt(8 * log(2)) * sigma.

### xpos

The center of the gaussian on the x0 axis.

### ypos

The center of the gaussian on the x1 axis.

### ellip

The ellipticity of the gaussian.

### 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.

The functional form of the model for points is:

```f(x0,x1) = ampl * exp(-4 * log(2) * 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)```

The grid version is evaluated by adaptive multidimensional integration scheme on hypercubes using cubature rules, based on code from HIntLib (  ) and GSL (  ).

•  HIntLib - High-dimensional Integration Library http://mint.sbg.ac.at/HIntLib/
•  GSL - GNU Scientific Library http://www.gnu.org/software/gsl/

## Bugs

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