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Next: COD
Up: Fortran interface
Previous: The DEMO program
The calling sequences for the four subroutines required to create
a user component are:
SUBROUTINE UINFO(IPAR, CNAME, NPAR)
INTEGER IPAR, NPAR
CHARACTER CNAME*(*)
C---
C IPAR I The parameter number.
C CNAME O The name of the parameter IPAR. Note if IPAR=0, then
C -return the name of the model.
C NPAR O The number of parameters in your user model.
C---
C*********
SUBROUTINE ULIMIT(PVAL, PLIM, NT, NPAR)
REAL PVAL(*), PLIM(3,*)
INTEGER NT, NPAR
C---
C PVAL(*) I/O The current parameter values
C PLIM(1,*) I If <0 then the corresponding parameter is frozen
C NT I Pointer to first parameter value in array PVAL(*)
C NPAR I Number of parameters
C---
C*********
REAL FUNCTION UFNY(X, PVAL, NT, NPAR)
REAL X, PVAL(*)
INTEGER NT, NPAR
C---
C X I The current X value
C PVAL I The current parameter values
C NT I Pointer to first parameter value in array PVAL(*)
C NPAR I Number of parameters
C---
C*********
SUBROUTINE UDERIV(X, PVAL, PLIM, DERIV, NT, NPAR)
REAL X, PVAL(*), PLIM(3,*), DERIV(*)
INTEGER NT, NPAR
C---
C X I The current X value
C PVAL I The current parameter values
C PLIM I The constraints array
C DERIV O The calculated derivative
C NT I Pointer to first parameter value in array PVAL(*)
C NPAR I Number of parameters
C---
The file XANADU:[LIB.UFNY]UFNYDEMO.FOR contains the source
code for the built-in DEMO user component. You should copy
that file and use it as a template for any file that you create.
When FIT starts, it calls UINFO with IPAR set equal to 0 to get the
name of the user component and the number of parameters. This component
name will be included in the names of the built-in components, and
therefore, should not match any existing component name (such as CONS,
LINE, etc.) If the user component is selected, then UINFO
will be called for each parameter to get the name of that parameter.
ULIMIT is always called after any parameter values have been changed
and before UFNY is called.
The purpose of ULIMIT is two-fold.
First, it should check the parameter values in PVAL and adjust
any that may cause a problem in UFNY (for example, if UFNY divides
by a parameter value, then ULIMIT should ensure that the parameter
does not equal zero).
Second, ULIMIT can be used to set up any initial data that UFNY needs.
Since, UFNY is often called many times with the same parameter set,
this can result in a speedup.
The parameter values are stored in PVAL(NT) to PVAL(NT+NPAR-1).
The PLIM array contains SIG, PLO, and PHI.
If PLIM(1,I) is less than zero,
then that parameter is frozen and you should not adjust the parameter
value.
Also, if PLIM(2,I)<PLIM(3,I), then an effective range
is active and you should not adjust a parameter outside that range.
UFNY is the function that actually calculates user component at
location X with parameter values given by PVAL.
UDERIV should calculate the derivative of the UFNY function with respect
to each parameter. The version contained in UFNYDEMO.FOR
evaluates the derivative numerically and hence you may be able to
use it without modification. If you use that method you should try
to scale the problem so that parameter values are in the range .1-100,
values outside this range work, but the convergence can be slower.
If PLIM(1,I)=-1 then that parameter is frozen and hence you do not
need to calculate the derivative. If PLIM(1,I)<-1 then the parameter
has been set equal to another parameter and you should calculate the
derivative in the normal manner (the FIT routine assumes that the
derivative has been correctly calculated).
If you able to compute the analytic derivative of your function with
respect to the parameter values, then you should use it, as an accurate
derivative can greatly improve the fitting process. NOTE, slow
convergence is most often due to the derivative being incorrectly
calculated. If you find that c2 drops slowly, and
that FIT is
unable to precisely locate the minimum, then you should carefully
check both your equations and the UDERIV implementation for typical
errors, such as an incorrect sign.
Once you have a working function, you should test it in PLT.
Use the MOdel ? command to see if your component is listed.
If not make sure you have linked a new version,
and that your are running that new version.
Next define a model that is composed only of your new component,
and enter a resonable set of parameters.
Do not attempt to fit at this time,
but rather just plot the data and model.
Use the Fit Plot 200 command to ensure that the function is
evaluated at 200 points over the visible range.
Is the plotted function what you expected?
If it is not then you should carefully examine your code.
Once the function is doing what you expect, then you can try to fit
it. If certain parameter values can cause a program crash, then you
should write a version of ULIMIT that prohibits these values.
   
Next: COD
Up: Fortran interface
Previous: The DEMO program
Web Page Maintained by: Dr. Lawrence E. Brown elwin@redshift.gsfc.nasa.gov
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