Create a simple source model expression containing one model component:

sherpa> PARAMPROMPT OFF
Model parameter prompting is off
sherpa> POLYNOM1D[modela]
sherpa> SOURCE 1 = modela

The last command in this series assigns a model expression to the source model for dataset number 1. This model expression contains one model component, modela (which is an arbitrary name that the user has given to the Sherpa model component POLYNOM1D).

Create a source model expression containing multiple model components:

sherpa> ATTEN[modelm]
sherpa> BBODY[modelh]
sherpa> SOURCE 1 = modelm * modelh

This example establishes two model components, modelm and modelh (which are arbitrary names that the user has given to the Sherpa model components ATTEN and BBODY, respectively). The last command assigns the model expression modelm * modelh to the source model for dataset number 1. The following commands each assign various other model expressions to source models for other datasets:

sherpa> SOURCE 2 = 10*(modelm + modelh)
sherpa> SOURCE 3 = (modelm - modelh)/2
sherpa> SOURCE 4 = 0.5*modelm + 0.7*modelh

Create a source model expression and establish model components simultaneously:

sherpa> ERASE ALL
sherpa> SOURCE 1 = ATTEN[modelm] * BBODY[modelh]

In this example the user assigns the model expression ATTEN[modelm] * BBODY[modelh] to the source model for dataset number 1.

Create a background model expression:

sherpa> ERASE ALL
sherpa> PARAMPROMPT ON
Model parameter prompting is on
sherpa> BACKGROUND = (POW[modelc])/2
modelc.gamma parameter value [0]
modelc.ref parameter value [1]
modelc.ampl parameter value [1]

This command assigns the model expression (POW[modelc])/2, to the background model for dataset number 1. In this example, the user accepted the initial guessed values for all of the parameters using the <RETURN> key.

Create a source model expression that includes a nested model:

sherpa> PARAMPROMPT OFF
Model parameter prompting is off
sherpa> shape = GAUSS
sherpa> SIN[modeli]
sherpa> COS[modelj]
sherpa> SRC = modeli{shape} + modelj

The second command, shape = GAUSS, creates a model stack. The commands SIN[modeli] and COS[modelj] establish and assign names to the Sherpa model components SIN and COS, respectively. The final command assigns the model expression modeli{shape} + modelj, to the source model for dataset number 1. Note that modeli will be evaluated on the output of the model expression shape, i.e., SRC = SIN(GAUSS(x)) + COS(x).

Create a source model expression involving joint mode 2-D models:

sherpa> DATA example_img.fits FITSIMAGE
sherpa> POLYNOM1D[modelaForAxis1]
sherpa> GAUSS[modelbForAxis2]
sherpa> SRC = modelaForAxis1{x1}*modelbForAxis2{x2}

The command POLYNOM1D[modelaForAxis1] assigns the name modelaForAxis1 to the Sherpa model component POLYNOM1D; likewise the command GAUSS[modelbForAxis2] assigns the name modelbForAxis2 to the Sherpa model component GAUSS. The final command assigns the model expression modelaForAxis1{x1}*modelbForAxis2{x2}, to the source model for dataset number 1. This model expression is an algebraic combination of joint-mode models.