Problems with a linked function

[Markus Michael Rau]

I just wrote a linked function to calculate the integral between two points.

It should basically do the same as the following octave function:

function [bins] = ber_bins(f, reds)
binsmaxindex = length(reds) - 1;
for i = 1:binsmaxindex
x(1) = reds(i);
x(2) = reds(i + 1);
y(1) = f(i);
y(2) = f(i + 1);
bins(i) = trapz(x, y);
endfor
endfunction

My c++ quellcode reads as follows:


#include <octave/oct.h>
#include <octave/parse.h>

DEFUN_DLD(my_bins, argv, ,"Usage: Calculates the bins"){
        octave_value_list retval;
        octave_value_list listzw;       
        octave_value zwisch;    
        int nargin = argv.length();
        if(nargin != 2){
        print_usage();
 
        }else{  
        ColumnVector f = argv(1).column_vector_value();
        ColumnVector red = argv(0).column_vector_value();
        ColumnVector x(2);
        ColumnVector y(2);
        octave_value_list listzw;       
        int binsmaxindex = f.length() - 1;
        ColumnVector bins(binsmaxindex);
        
        const double *redval = red.fortran_vec();
        const double *fval = f.fortran_vec();
        double  *xval = x.fortran_vec();
        double  *yval = y.fortran_vec();
        double *binsval = bins.fortran_vec();   
        for(int i = 0; i < binsmaxindex; ++i){
                
                xval[0] = redval[i];
                xval[1] = redval[i + 1];
                yval[0] = fval[i];
                yval[1] = fval[i + 1];
                listzw(0) = octave_value(x);
                listzw(1) = octave_value(y);    
                zwisch = feval("trapz",listzw, 1); 
                binsval[i] = zwisch.scalar_value();
        }
retval.append(octave_value(bins));

return retval;
}}

I get the following error if i for example call the function:

test = my_bins([1;2], [1;4])

error: octave_base_value::double_value (): wrong type argument `list'

I just don't see the type list in the documentation 
http://www.gnu.org/software/octave/doc/interpreter/Matrices-and-Arrays-in-Oct_002dFiles.html#Matrices-and-Arrays-in-Oct_002dFiles

How can I solve the problem?

Thanks for your support,

Markus


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