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Establishes a model component and its parameters,
for use in the current Sherpa session.
sherpa> [CREATE] <sherpa_modelname>
(The brackets around CREATE indicate that its use is optional; see
examples below.) In addition, Sherpa provides the user with the ability
to both establish a model component, and to assign to it an arbitrary
name:
sherpa> [CREATE] <sherpa_modelname>[<modelname>]
where <sherpa_modelname>is the Sherpa default model name (or an XSPEC
model name, with the prefix `xs' attached), and <modelname> is the name
being given to the model component by the user. Note that <modelname>
must be enclosed in brackets, [ ].
Sherpa's ability to assign arbitrary names to model components
allows the user to establish multiple independent models of
the same type during a single session, and is a valuable
feature of the software.
Note that an assigned model name can be any arbitrary string,
except a string that is already a Sherpa command.
By default, Sherpa will prompt the user for the
initial model component
parameter values. (Parameter prompting can be turned off using the command
PARAPROMPT OFF.)
At the model parameter prompt, the user may either:
-
Hit the <RETURN> key to
accept the given initial parameter value.
Note that if a dataset has not been input, then the initial parameter
values are arbitrary default values. However, if a dataset has been input,
then the initial parameter values are estimates based on the filtered data
and the defined instrument model
(see AUTOESTfor more information).
-
Hit the <RETURN> key to accept the
given initial parameter value, and subsequently set the
parameter value and range using one of the syntax options
whose descriptions may be found in
PARAMSET
(see CREATEPARAMSET).
-
Hit the <RETURN> to accept the
given initial parameter value, and subsequently set the
parameter value using the GETX or GETY command,
which allows the user to assign the value interactively from a plot.
-
Enter ,-1 to accept the given initial parameter value,
and to set the parameter to be
frozen. Note that there cannot be a space between the
, and the -1.
-
Enter <value>:<min>:<max>[:<delta>][,-1],
where:
| <value> | Model parameter initial value. |
| <min> | Minimum value for that parameter range. |
| <max> | Maximum value for that parameter range. |
| <delta> | Specifies initial parameter step size. |
| ,-1 | Sets the parameter to be frozen. |
Note that the default setting for
delta is 1% of the parameter value.
Otherwise, specifying delta will set the initial parameter
step size to an absolute value.
The parameter step size is used by the
optimization method to determine where to
sample parameter space. As such, if the value
of a parameter is known well, then specifying
a small delta may lead to a substantially faster
and better fit.
Note that this colon separated list need not include all of the elements, but
it does need to maintain the proper sequential order, and also include the
colons around skipped elements. Also, there cannot be a space between the
, and the -1.
The model components that have been established in the current Sherpa session,
and their parameter information,
may be listed with the command SHOW MODELS.
Note however that information about model parameter delta settings
is currently not returned by SHOW.
Information about model parameter delta settings
is included when using SAVE.
| Setting parameter values and ranges |
ahelp paramset, ahelp createparamset |
| Linking parameter values |
ahelp linkparam |
| Freezing and thawing model parameters |
ahelp freeze, ahelp thaw |
| How parameter value estimates are made |
ahelp autoest, ahelp guess |
| Controlling model integration |
ahelp integrate |
| Creating model expressions |
ahelp modelexpr |
| Creating model stacks |
ahelp modelstack |
| Creating nested models |
ahelp nestedmodels |
| Creating joint-mode models |
ahelp jointmode |
Establish a model component
sherpa> CREATE POLY
POLY.c0 parameter value [1]
POLY.c1 parameter value [0]
POLY.c2 parameter value [0]
POLY.c3 parameter value [0]
POLY.c4 parameter value [0]
POLY.c5 parameter value [0]
POLY.c6 parameter value [0]
POLY.c7 parameter value [0]
POLY.c8 parameter value [0]
POLY.offset parameter value [0]
The command CREATE POLY establishes the
Sherpa modelPOLY
as a model component
available for use in the current Sherpa session.
Note that after issuing this command, the user is prompted for
the initial model parameter values.
In this example, the user accepted the given initial values for
all of the parameters, using the <RETURN> key.
The following command is equivalent:
Establish a model component, and assign it a name:
sherpa> CREATE POLY[modela]
modela.c0 parameter value [1]
modela.c1 parameter value [0]
modela.c2 parameter value [0]
modela.c3 parameter value [0]
modela.c4 parameter value [0]
modela.c5 parameter value [0]
modela.c6 parameter value [0]
modela.c7 parameter value [0]
modela.c8 parameter value [0]
modela.offset parameter value [0]
The command CREATE POLY[modela] establishes
the Sherpa model
component POLY,
and assigns to it the name modela.
Note that after issuing this command, the user is prompted for
the initial model parameter values.
In this example, the user accepted the given initial values for
all of the parameters, using the <RETURN> key.
The following command is equivalent:
Establish a model component, assign it a name, set parameter values and ranges
including initial parameter step size, and freeze a parameter:
sherpa> GAUSS[modelb]
modelb.fwhm parameter value [10] 2.0:1:10:0.5
modelb.pos parameter value [0] 1:0.1:
modelb.ampl parameter value [1] 3::100:2,-1
This example establishes and assigns the name modelb to
the Sherpa
model component GAUSS1D.
Note that in this example the user entered an initial value of 2.0,
a minimum range value of 1, a maximum range value of 10, and an
initial parameter step size delta of 0.5 for parameter
fwhm; entered a value of 1, and a minimum range value of 0.1
for parameter pos;
and entered a value of 3, a maximum range value of 100, and an initial parameter
step size of 2 for parameter ampl, and froze this parameter.
Establish a model component, assign it a name, set parameter values and ranges,
and freeze a parameter:
sherpa> GAUSS[modelbb]
modelbb.fwhm parameter value [10] 2.0:1:10
modelbb.pos parameter value [0] 1:0.1:
modelbb.ampl parameter value [1] 3::100,-1
This example establishes and assigns the name
modelb to the Sherpa
model component GAUSS1D.
Note that in this example the user entered an initial value of 2.0,
a minimum range value of 1, and a maximum range value of 10 for parameter
fwhm; entered a value of 1, and a minimum range value of 0.1 for
parameter pos;
and entered a value of 3, and a maximum range value of 100 for parameter
ampl, and froze this parameter (note that after the maximum range
value, specification of initial parameter step size delta is
optional and may be omitted).
Establish an XSPEC
model component, assign it a name, and freeze a parameter:
sherpa> XSBBODY[modeld]
modeld.kT parameter value [3]
modeld.norm parameter value [1] ,-1
This command establishes and assigns the name modeld to the
XSPEC model component
bbody.
In this example, the user
accepted the given initial values for all of the parameters, using
the <RETURN>,
and set parameter norm to be frozen.
Turn off model parameter prompting; establish a model component and
assign it a name:
sherpa> PARAMPROMPT OFF
Model parameter prompting is off
sherpa> POW[modelc]
The first command turns off prompting for model parameter values.
The second command establishes the Sherpa model
component POW, and
assigns to it the name modelc. Since parameter prompting was
turned off, the
model is automatically established using the given initial values for all
of the parameters.
Establish two independent model components of the same type:
sherpa> ERASE ALL
sherpa> PARAMPROMPT ON
Model parameter prompting is on
sherpa> POW[modelc]
modelc.gamma parameter value [0] 1.0
modelc.ref parameter value [1]
modelc.ampl parameter value [1]
sherpa> POW[modelc2]
modelc2.gamma parameter value [0] 2.0
modelc2.ref parameter value [1]
modelc2.ampl parameter value [1]
The third command establishes the Sherpa model component
POWLAW1d,
and assigns to it the name modelc. In this example, the user set
parameter
gamma of model component modelc to the value of 1.0.
The last command establishes another Sherpa model
component POWLAW1d,
and assigns to it the name modelc2. In this example, the user set
parameter
gamma of model component modelc2 to the value of 2.0.
Note that model components modelc
and modelc2 are independent of one another.
- sherpa
-
autoest,
background,
create_model,
createparamset,
fit,
freeze,
get_defined_models,
get_model_params,
get_models,
get_num_par,
get_par,
get_stackexpr,
getx,
gety,
guess,
instrument,
integrate,
is_paramset,
jointmode,
kernel,
lineid,
linkparam,
mdl,
modelexpr,
modelstack,
nestedmodel,
noise,
paramprompt,
paramset,
pileup,
rename,
run_fit,
set_par,
set_paramset,
set_stackexpr,
source,
thaw,
truncate,
unlink
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