segmentation fault in image processing using SURF

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I am getting a segmentation fault after the loop runs for sometime. I want the loop to run as an infinite loop. Why is the error occurring?

int main( int argc, char** argv ) {

cv::VideoCapture cap("tcp://192.168.1.1:5555"); // open a video file

if(!cap.isOpened()) // check if succeeded { std::cout << " not found or could not be opened" << std::endl; printf("4\n"); return -1; }

unsigned long counter =0; cv::Mat frame; // read frames until end of video:

struct timeval start,end; long seconds,useconds; long mtime=0; gettimeofday(&start,NULL); cap >> frame; imwrite("image.pgm",frame); Mat img_1 = imread( "image.pgm" ); int minHessian = 500;

SurfFeatureDetector detector( minHessian,1,2,false,true ); detector.detect( img_1, keypoints_1p );

SurfDescriptorExtractor extractor(minHessian,1,1,1,0); Mat descriptors1, descriptors2;

extractor.compute(img_1, keypoints_1p, descriptors1);

while(cap.read(frame)) {

// adjust the filename by incrementing a counter
      std::stringstream filename (std::stringstream::in | std::stringstream::out);
      filename << "img-000" <<  counter++ << ".pgm";

//printf("filename =%s ",filename);
      std::cout << "writing " << filename.str().c_str() << " to disk" << std::endl;

// save frame to file: image0.jpg, image1.jpg, and so on...
     cv::imwrite(filename.str().c_str(),frame);





Mat img_2 = imread( filename.str().c_str() );

 if( !img_1.data || !img_2.data )
  { 
   std::cout<< " --(!) Error reading images " << std::endl; return -1;
  }

//-- Step 1: Detect the keypoints using SURF Detector

detector.detect( img_2, keypoints_2p);

// computing descriptors

extractor.compute(img_2, keypoints_2p, descriptors2);

int i,j;

Mat a(descriptors1.rows,descriptors1.cols,descriptors1.type()); Mat b(descriptors2.rows,descriptors2.cols, descriptors2.type()); a=descriptors1; b=descriptors2;

Mat m(descriptors1.rows,2,CV_16U);

if(((descriptors2.rows)||(descriptors1.rows))==0) { m.push_back(0); return 0; }

Mat des2t(descriptors2.rows,descriptors2.cols,descriptors2.type());

des2t= b.t();

m= Mat::zeros(descriptors1.rows,1,CV_32F);

Mat dotprod = (descriptors1*des2t);

Mat angle(dotprod.rows,dotprod.cols,dotprod.type());

for(int k=0;k<dotprod.rows;k++) {="" for(int="" l="0;l&lt;dotprod.cols;l++)" {<="" p="">

                 angle.at<float>(k,l)= acos(dotprod.at<float>(k,l));

         }

}

int jmin,jmin2;

float minangle,min2; for(i=0;i< dotprod.rows;i++) { minangle=angle.at<float>(i,0); jmin=1; min2=angle.at<float>(i,0); jmin2=1; for(j=1;j<dotprod.rows;j++) {<="" p="">

           if(minangle > angle.at<float>(i,j))
           {
                minangle=angle.at<float>(i,j);             
                jmin=j;

           }

           if((min2>angle.at<float>(i,j)) && (angle.at<float>(i,j) > minangle))
           {
                min2=angle.at<float>(i,j);             
                jmin2=j;

           }


     }
     if(minangle < 0.8*min2)
     {
     m.at<int>(i,0)=jmin;
     //m.at<int>(i,0)=i;
     } 
     else
     {
      m.at<int>(i,0)=jmin2;
      //m.at<int>(i,0)=i;
     }

}

vector <point2f> im1; vector <point2f> im2;

for(int z=0;z<= descriptors2.rows;z++) { for(int y=0;y<=descriptors2.cols;y++) {

     im2.push_back(keypoints_2p[descriptors2.at<float>(z,y)].pt);

} }

for( int z=0;z<= descriptors1.rows;z++) { for( int y=0;y<=descriptors1.cols;y++) {

     im1.push_back(keypoints_1p[descriptors1.at<float>(z,y)].pt);

} } //calculate the dx and dy for all features int v; vector <float> dx,dy ... (more)