AHELP for CIAO 4.11 Sherpa v1

# emissiongaussian

Context: models

## Synopsis

Gaussian function for modeling emission.

## Syntax

`emissiongaussian`

## Description

It is for use when the independent axis is in Angstroms.

## Example

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

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

```mdl
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.flux     thawed            1 -3.40282e+38  3.40282e+38
mdl.skew     frozen            1  1.17549e-38  3.40282e+38           ```

### ATTRIBUTES

The attributes for this object are:

### fwhm

The full-width half-maximum of the model in km/s.

### pos

The center of the gaussian, in Angstroms.

### flux

The normalisation of the gaussian.

### skew

The skew of the gaussian.

### limit

The model is only evaluated for points that lie within limit sigma of pos. It is a hidden parameter, with a default value of 4.

The functional form of the model for points is:

```f(x) = flux * exp(-0.5 * d(x)^2) / s2   if skew = 1

= 2 * flux * exp(-0.5 * d2(x)^2) / (s2 * (1 + skew))

otherwise

d(x) = (x - pos) / s

d2(x) = d(x)                  if x <= pos

= d(x) / skew           otherwise

s2 = 2.50662828 * s

s = 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 0.

## Bugs

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