NAME

PDL::Fit::Levmar::Func - Create model functions for Levenberg-Marquardt fit routines

DESCRIPTION

This module creates and manages functions for use with the Levmar fitting module. The functions are created with a very simple description language (that is mostly C), or are pure C, or are perl code. For many applications, the present document is not necessary because levmar uses the Levmar::Func module transparantly. Therefore, before reading the following, refer to PDL::Fit::Levmar.

SYNOPSIS

    use PDL::Fit::Levmar::Func;

   $func = levmar_func(  FUNC =>  # define and link function

 '
  function gaussian
  loop
  x[i] = p[0] * exp(-(t[i] - p[1])*(t[i] - p[1])*p[2]);
  end function

  jacobian jacgaussian
  double arg, expf;
  loop
  arg = t[i] - p[1];
  expf = exp(-arg*arg*p[2]);
  d0 = expf;
  d1 = p[0]*2*arg*p[2]*expf;
  d2 = p[0]*(-arg*arg)*expf;
  end jacobian 
  ' 
  );

  $hout = PDL::Fit::Levmar::levmar($p,$x,$t,  # fit the data
               FUNCTION => $func,
 );

FUNCTIONS

levmar_func()

 levmar_func( OPTIONS )

This function creates and links a function, ie, takes a function definition and returns a function (object instance) ready for use by levmar. see PDL::Fit::Levmar::Func for more information.

OPTIONS:

 Some of the options are described in the PDL::Fit::Levmar documentation.

 MKOBJ  -- command to compile source into object code. This can be set.
        The default value is determined by the perl installation and can
        be determined by examining the Levmar::Func object returned by 
        new or the output hash of a call to levmar. A typical value is
        cc -c -O2 -fPIC -o %o %c

 MKSO   -- command to convert object code to dynamic library code. A typical
         default value is
         cc -shared -L/usr/local/lib -fstack-protector %o -o %s
 

 CTOP  --   The value of this string will be written at the top of the c code
  written by Levmar::Func. This can be used to include headers and so forth.
  This option is actually set in the Levmar::Func object.

call()

Call (evaluate) the fit function in a Levmar::Func object.

 use PDL::Fit::Levmar::Func;

 $Gh = levmar_func(FUNC=>$fcode);

 $x = $Gh->call($p,$t);

 Here $fcode is a function definition (say lpp code). (This does
 not currently work with perl subroutines, I think. Of course,
 you can call the subroutine directly. But it would be good
 to support it for consistency.)
 
 $p is a pdl or ref to array of parameters.
 $t is a pdl of co-ordinate values.
 $x is the fit function evaluated at $p and $t. $x has the
 same shape as $t.

 $Gf = levmar_func( FUNC => '
       function    
       x = p0 * t * t;
     ');

 print $Gf->call([2],sequence(10))  , "\n";
 [0 2 8 18 32 50 72 98 128 162]

new

  my $fitfunc = new PDL::Fit::Levmar::Func(...);
  or
  my $fitfunc = levmar_func(...);

Generic constructor. Use levmar_func rather than new.

AUTHORS

Copyright (C) 2006 John Lapeyre. All rights reserved. There is no warranty. You are allowed to redistribute this software / documentation under certain conditions. For details, see the file COPYING in the PDL distribution. If this file is separated from the PDL distribution, the copyright notice should be included in the file.