matlab - c code translation

Hello, I'm trying to translate my code from Matlab to C in a mex file. But I encoutered some difficulties because Matlab has predefined functiones for almost everything.So this is my Matlab code:

% m=40;
% n=20;
%  rap_V = abs(randn(m,n))
%   for i = 4:m-3
%      for j = 4:n-3
%         
%         im_A = rap_V(i-3:i+3,j-3:j+3);
%         im_A = im_A(:);

And my C code from the mex file:

#include "math.h"
#include "mex.h"   //--This one is required

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
//Declarations
mxArray *xData;
double *xValues, *outArray;
int i,j,ii,jj,iii;
int rowLen, colLen;

//Copy input pointer x
xData = prhs[0];

//Get matrix x
xValues = mxGetPr(mxGetPr(xData));
rowLen = mxGetN(xData);
colLen = mxGetM(xData);

//Allocate memory and assign output pointer
plhs[0] = mxCreateDoubleMatrix(7*7, 1, mxREAL); //mxReal is our data-type

//Get a pointer to the data space in our newly allocated memory
outArray = mxGetPr(plhs[0]);

//Copy matrix while multiplying each point by 2
for(i=4;i<rowLen-3;i++)
{
    for(j=4;j<colLen-3;j++)
    {   int con=0;
        for(ii=i-3; ii<=i+3; ii++)
            for(jj=j-3; jj<=j+3; jj++)
             {outArray[con] = xValues[(ii*7)+jj];
              con=con+1;
              }

        }

}

My main problem is this line :

outArray[con] = xValues[(ii*7)+jj];

because it doesn't copy the right values of the input matrix into the 49*1 outArray. The aim is to copy the 7*7 matrixes into a 49*1 which I should use further on in my project. Any ideeas? }

[Jan]

Please apply a proper code formatting as explained in the "Markup help" link on this page. Currently your code is not readable.

Answer 1

[Titus Edelhofer]

Hi,

note that MATLAB sorts the values by column, i.e., you should use

xValues[rowLen*jj+ii]

instead.

Titus

Answer 2

[Jan]

This is one mexGetPr to much:

double *xValues;
mxArray *xData;
xData = prhs[0];
// xValues = mxGetPr(mxGetPr(xData));  % ERROR
xValues = mxGetPr(xData);