Re: Convert double to octave_value for assignment to column vector

[babelproofreader]

More problems :-(  My code now is shown below.

#include <octave/oct.h>
#include <octave/dColVector.h>
#include <octave/parse.h> // necessary for the call to feval
#include <octave/ov.h> // necessary for conversion to double

DEFUN_DLD (rep_median_compile, args, , "Input is a column vector of values,
output is a repeated median straight line fit of these values.")
{
    octave_value_list retval_list;

    if (args(0).length () < 1)
    {
        error ("Invalid arguments");
        return retval_list;
    }
    ColumnVector rep_median_compile_input = args(0).column_vector_value ();
// input vector
    ColumnVector rep_median_compile_output = rep_median_compile_input; //
copy of input vector to hold repeated median straight line fit

    if (error_state)
    {
        error ("Invalid arguments");
        return retval_list;
    }

    octave_value_list median_calc_return; // declare an octave value to hold
output of feval call to Octave median function
    double slope; // declare a double value to hold final value of slope
    double intercept; // declare a double value to hold final value of
intercept
    OCTAVE_LOCAL_BUFFER (double, i_slopes, args(0).length ()-1 ); // array
to hold individual point-to-point slopes
    OCTAVE_LOCAL_BUFFER (double, i_intercepts, args(0).length ()-1 ); //
array to hold individual point-to-point intercepts
    OCTAVE_LOCAL_BUFFER (double, slope_medians, args(0).length () ); //
array to hold medians of non-matched point-to-point slopes
    OCTAVE_LOCAL_BUFFER (double, intercept_medians, args(0).length () ); //
array to hold medians of non-matched point-to-point intercepts
    int jj_tmp_count; // non-matched point-to-point count for filling above
arrays (necessary because of jj != ii loop condition)

    for (octave_idx_type ii (0); ii < args(0).length (); ii++) 
    {

      jj_tmp_count = 0; // initialise to 0 for each separate ii loop

        for (octave_idx_type jj (0); jj < args(0).length (); jj++)
        {

             if (jj != ii) // condition avoids matching a point to itself!
             {
                i_slopes[jj_tmp_count] = ( rep_median_compile_input(jj) -
rep_median_compile_input(ii) ) / ( (jj) - (ii) ); // slope between distinct
points

                i_intercepts[jj_tmp_count] =  rep_median_compile_input(jj) -
( i_slopes[jj_tmp_count] * jj ); // calc intercept b = y - mx

                jj_tmp_count = jj_tmp_count + 1; // increment counter only
when condition avoids matching a point to itself!
             }

        }                
                median_calc_return = feval ( "median", octave_value (i_slopes) 
);
                slope_medians[ii] = median_calc_return(0).double_value ();

                median_calc_return = feval ( "median", octave_value
(i_intercepts) );
                intercept_medians[ii] = median_calc_return(0).double_value
();
    }    
        median_calc_return = feval ( "median", octave_value (slope_medians) );
        slope = median_calc_return(0).double_value (); 

        median_calc_return = feval ( "median", octave_value
(intercept_medians) );
        intercept = median_calc_return(0).double_value (); 

    for (octave_idx_type ii (0); ii < args(0).length (); ii++) // loop to
fill output column_vector with repeated_median line fit values
    {
        rep_median_compile_output(ii) = slope * (ii) + intercept;
    }

    retval_list(0) = rep_median_compile_output;

    return retval_list;
}

This compiles without giving error warnings, and even gives an output when
called as a function, but the output is obviously wrong, giving a fitted
line of y=mx for any input. I cannot see where the code is going wrong, but
I'm certain the fault is not with the algorithm as the exact same algorithm
works OK as a .m file.
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