From help-octave-request at bevo dot che dot wisc dot edu Mon Nov  3 09:03:31 2003
Subject: Re: Octave segfaults on .oct file + more troubles
From: Paul Kienzle <pkienzle at jazz dot ncnr dot nist dot gov>
To: Martijn Brouwer <eambrouwer at myrealbox dot com>
Cc: octave <help-octave at bevo dot che dot wisc dot edu>
Date: Mon, 3 Nov 2003 10:03:24 -0500

On Sun, Nov 02, 2003 at 12:23:01AM +0100, Martijn Brouwer wrote:
> I have problems compiling and running an .oct file with the following code:
> 
> #include <oct.h>
> #include <complex>
> #include <cmath>
> using namespace std;
> 
> #define pi 3.141592654
> 
> DEFUN_DLD(lgm, args, ,"Calculates layer matrix from layer thickness, wavelength, refractive index and cos(th)") {
> 	complex<double> n(args(0).complex_value());
> 	double d=args(1).double_value();
> 	double l=args(2).double_value();
> 	complex<double> cosan(args(3).complex_value());
> //	complex<double> expbeta=exp(-2*pi*n*d*cosan/l);
> //	complex<double> expbeta=2
> 	double expbeta=2;
> 
> 	ComplexMatrix LGM;
> 	LGM(0,0)=expbeta;
> 19    LGM(1,1)=1/expbeta;
> 
> 	return octave_value(LGM);
> }

The main problem you are experiencing is that 
	1/std::complex<double>
is not defined.  This is easily addressed using
	1./std::complex<double>

The second thing is that you should preallocate
your arrays:

	ComplexMatrix LGM(2,2);

Then there are a number of stylistic issues
such as error checking use of octave types.

The following code compiles and runs for me
(octave-2.1.50 on Debian with gcc 3.3.2):

#include <oct.h>

#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

DEFUN_DLD(lgm, args, ,"Calculates layer matrix from layer thickness, wavelength, refractive index and cos(th)") 
{
  octave_value_list retval;
  if (args.length() != 4) 
    { 
      print_usage("lgm"); 
      return retval; 
    }
  Complex n(args(0).complex_value());
  double d=args(1).double_value();  
  double l=args(2).double_value();
  Complex cosan(args(3).complex_value());
  if (error_state) return retval;

  Complex expbeta=exp(-2.*M_PI*n*d*cosan/l);

  ComplexMatrix LGM(2,2);
  LGM(0,0)=expbeta;
  LGM(1,1)=1./expbeta;

  return octave_value(LGM);
}

By the way, you won't see much speed improvement
building the matrices in an oct-file.  Instead
you will want to build the layer matrices on
the fly as you are calculating the reflectivity
from your layer model so that the nested for loops
are in C rather than octave.

Paul Kienzle
pkienzle at nist dot gov



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