Defines the source model expression to be used for fitting a dataset.
The command SRC is an abbreviated equivalent.
sherpa> SOURCE [<dataset range> | ALLSETS] = <modelExpr>
<dataset range> = # (or more generally #:#,#:#, etc.) such that #
specifies a dataset number and #:# represents an inclusive range of
datasets; one may specify multiple inclusive ranges by separating them
with commas. The default dataset is dataset 1.
The model expression,
<modelExpr>,
is an algebraic combination of one or more of the following elements:
{<sherpa_modelname> | <sherpa_modelname>[modelname] |
<modelname> | <model_stack> | <nested_model>}
along with numerical values. The following operators are
recognized: + - * / ( ) { }.
See the CREATE command for further information.
Note that:
-
The documentation on
Sherpa Models contains a
summary list, and descriptions, of the models
that are available within Sherpa, which include models
from XSPEC, v. 11.3.
-
By default, if the model expression includes a model
component that has not previously been established, Sherpa
will prompt for the initial parameter values for that model component.
This prompting can be turned off using the
PARAMPROMPT OFF command.
To reset a source model stack, issue the command:
sherpa> SOURCE [<dataset range> | ALLSETS] =
Establish a model component, and define it as the source model to be
used for fitting a specific dataset:
sherpa> SOURCE 2 = GAUSS
GAUSS.fwhm parameter value [10]
GAUSS.pos parameter value [0]
GAUSS.ampl parameter value [1]
sherpa>
This command defines the Sherpa model GAUSS
as the source model to be used for fitting dataset number 2.
Note that the user accepted the given initial values for
all of the parameters, using the <RETURN> key.
Establish a model component and assign it a name; define the model component
as the source model to be used for fitting a specific dataset:
sherpa> PARAMPROMPT OFF
Model parameter prompting is off
sherpa> GAUSS[modelb]
sherpa> SOURCE 2 = modelb
In the first command, the name modelb is given to
the Sherpa model component GAUSS
(see the CREATE command for more information
on the model language syntax). The second command defines
this model as the source model to be used for fitting dataset
number 2.
Establish model components, and assign them names;
create a source model expression to be used for fitting a specific dataset:
sherpa> POW[modelc]
sherpa> GAUSS[modelf]
sherpa> SOURCE 1 = modelc + modelf
The last command in this series assigns
the model expression modelc + modelf
as the source model to be used for fitting dataset number 1.
The following commands each assign
various other model expressions
to source models for dataset numbers 2, 3, and 4 respectively:
sherpa> SOURCE 2 = 10*(modelc + modelf)
sherpa> SOURCE 3 = (modelc - modelf)/2
sherpa> SOURCE 4 = 0.5*modelc + 0.7*modelf
See the CREATE command for further
information about creating model expressions.
Establish a model component, assign it a name, and define it as the
source model to be used for fitting:
sherpa> ERASE ALL
sherpa> SOURCE 1 = POW[modelc]
In this single command, the name modelc is assigned to the
Sherpa model component POW,
and then this model is defined as the
source model to be used for fitting dataset number 1.
Establish model components, assign them names, and use them to define a
source model expression to be used for fitting:
sherpa> ERASE ALL
sherpa> SOURCE 2 = GAUSS[modelb] + POW[modelc]
In this single command, the following is performed:
the name modelb is assigned to the Sherpa model
component GAUSS;
the name modelc is assigned to the Sherpa model
component POW;
a model expression, which here is the sum of these two models components,
is defined as the source model to be used for fitting dataset
number 2.
Establish a model component,
assign it a name, define the parameters, and define it as the source model
to be used for fitting:
sherpa> ERASE ALL
sherpa> SOURCE = POLY[modela](3.0:1.0:4.0)
With this single command, the name modela is assigned to the
Sherpa model component POLY,
the value of 3.0 is given to the model's first
parameter (in this case parameter c0),
the minimum of 1.0 is set for this parameter,
the maximum of 4.0 is set for this parameter,
and then this model is defined as the
source model to be used for fitting dataset number 1.
Establish multiple model
components, assign them names, and use them in a source model
expression definition:
sherpa> SOURCE 2 = GAUSS[modelb](3:2.5:4.403, 1:-10:10, 1:-3.5:3.5)
+ POW[modelc]
With this single command, the following is performed:
the name modelb is assigned to the Sherpa model
component GAUSS;
various parameter values and ranges are set for the parameters of modelb;
the name modelc is assigned to the Sherpa model
component POW; a
model expression,
which is the sum of these two models,
is defined as the source model to be used for fitting dataset number 2.
Establish continuum and line model stacks, and combine these stacks into
a source model expression definition:
sherpa> PARAMPROMPT OFF
sherpa> CONT = POWLAW1D[modeld]
sherpa> ELINE = NGAUSS[modele]
sherpa> SOURCE = CONT + ELINE
In the second and third commands, the names modeld and
modele are assigned to the
Sherpa model components POWLAW1D
and NGAUSS respectively; these model components are then
assigned to the user-defined model stacks CONT and
ELINE. These model stacks are then assigned to
the source model expression.
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