Calling a octave function from a fortran function that accepts a function as an argument

[John Weatherwax]

Hello,
   I am having trouble with "Calling a octave function from a fortran 
function that accepts a function as an argument"

   Details:
   Many FORTRAN routines (think quadrature or ODE's) require a function 
to be given at the same time as the  computational routine .  Does 
anyone have a SIMPLE example of how to create an *.oct file that will 
allow an octave function to be called from the FORTRAN computational 
routine? 

For instance in octave (testfun.m):

function [ res ] = testfun( x )
 res = sin( x ) ;
endfunction

In FORTRAN (fortsub2.f):

     subroutine fortsub2(f,xin,nxin,xout)
C     Call f(.) on every element of xin:
C     return in xout:
     external f
     real*8 xin(*),xout(*)
     integer*4 nxin
     do i=1,nin
        xout(i)=f(xin(i))
     enddo
     return
     end

Now in C++ I have been unsuccessfull in creating the *.cc file to make 
an *.oct file with mkoctfile.  I want to call the routine with something 
like:

> xin = rand( 4,1 );
> [ xout ] = exOct2FortFnCall( "testfun", xin );

The result in xout should be xout = sin( xin );

My feable attempt at this procedure is included below.  Any help 
pointers would be greatly appreciated.  I know there are source code 
examples for things like LSODE but I was hoping for a smaller example 
that I could play with.

TIA,

John

The C++ example call (exOct2FortFnCall.cc):

#include <octave/oct.h>
#include <octave/parse.h>
#include <octave/ov-fcn.h>

// Function pointer to octave/FORTRAN function:
octave_function *octFnPtr;

typedef (double) (*fort_fcn_ptr) (double*)

extern "C" int F77_FUNC(fortsub2,FORTSUB2)\
                      (fort_fcn_ptr,double*,int&,double*);

DEFUN_DLD(exOct2FortFnCall,args, , \
     "An example passing an octave function INTO a FORTRAN subroutine, \
          computing with it and returning the result to octave."){

 octave_value_list retval;

 // Extract input arguments into octave api/C++:
 //
 // Octave function name:
 std::string myfunc = args(0).string_value();
 // Octave xin:
 ColumnVector xin( args(1).vector_value() );
 double* xinptr = xin.fortran_vec();
 int nxin = args(1).length();

 // Extract the octave function into a pointer:
 octFnPtr = extract_function( myfunc, "Err: exOct2FortFnCall", "", "" );

 ColumnVector xout;
 double *xoutptr = xout.fortran_vec();

 F77_FUNC(fortsub2,FORTSUB2)(octFnPtr,xinptr,nxin,xoutptr);

 retval.append( xout );
}

--

John L. Weatherwax

Lincoln Laboratory, Massachusetts Institute of Technology
244 Wood Street
Lexington, MA 02420-9108 USA

Phone : 781-981-5370
Fax   : 781-981-4739
Email : address@hidden

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