Mex-Code crashes during for loop at certain iteration

Hello,

I wrote a mex function in order to speed up a calculation, but the code crashes whole MATLAB with a segmentation fault if I set the maximum iteration index too high.

Here is the code:

#include "mex.h"
#include "matrix.h"

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{

      //declarations
      float *time_series_matrix, *shapelet;
      mwSize minimum_bolus_arrival, maximum_bolus_arrival, number_of_time_series, length_time_series, length_shapelet;
      float *distance_matrix;
      mwSize a, i, j, start_column;
      float sum;

      //initializations
      time_series_matrix = (float *) mxGetData(prhs[0]);
      shapelet = (float *) mxGetData(prhs[1]);
      minimum_bolus_arrival = (mwSize) mxGetScalar(prhs[2]);
      maximum_bolus_arrival = (mwSize) mxGetScalar(prhs[3]);

      number_of_time_series = (mwSize) mxGetM(prhs[0]);
      length_time_series = (mwSize) mxGetN(prhs[0]);
      length_shapelet = (mwSize) mxGetN(prhs[1]);

      plhs[0] = mxCreateNumericMatrix(number_of_time_series, (maximum_bolus_arrival - minimum_bolus_arrival), mxSINGLE_CLASS, mxREAL);
      distance_matrix = (float *) mxGetData(plhs[0]);

      if(maximum_bolus_arrival > (length_time_series - length_shapelet))
          maximum_bolus_arrival = (length_time_series - length_shapelet);

      //for every pixel (for all time series)
      //time_series_matrix columnwise in memory

      for (i = 0; i < 1001; i++) {
          //get subsequence for each possible starting point
          mexPrintf("%d\n", i);
          for (j = minimum_bolus_arrival - 1; j < maximum_bolus_arrival; j++) {
              start_column = j - minimum_bolus_arrival + 1;
              sum = 0;
              for (a = 0; a < length_shapelet; a++) {
                  sum = sum + (shapelet[a] - time_series_matrix[i+j*number_of_time_series+a])*(shapelet[a] - time_series_matrix[i+j*number_of_time_series+a]);     
              }

              distance_matrix[i+start_column*number_of_time_series] = sum/length_shapelet;        
          }          
      }
  }

distance_matrix is an array of 3072*500 elements. Also time_series is of larger dimensions (3072*4096). I'm sure it's not an array boundary problem. What now happens is that if I set i < 1000, everything works fine and the returned array (distance_matrix) contains the expected values. If I set i < 1001, the crash occures.

Any ideas?

Thx

Answer 1

[Milka]

Found the bug myself. It was a boundary problem. Just at another counter variable than expected. The 2nd for loop should be

j<maximum_bolus_arrival - 1