title: Passing Python array to c++ function with SWIG
body: <p>I have written a good bit of code in python and it works great. But now I'm scaling up the size of the problems that I'm analyzing and python is dreadfully slow. The slow part of the python code is </p>
  
  <pre><code>    for i in range(0,H,1):
         x1 = i - length
         x2 = i + length
         for j in range(0,W,1):
            #print i, ',', j    # check the limits
            y1 = j - length
            y2 = j + length
            IntRed[i,j] = np.mean(RawRed[x1:x2,y1:y2])
  </code></pre>
  
  <p>With H and W equal to 1024 the function takes around 5 minutes to excute.  I've written a simple c++ program/function that performs the same computation and it excutes in less than a second with the same data size. </p>
  
  <pre><code>   double summ = 0;
     double total_num = 0;
     double tmp_num = 0 ;
     int avesize = 2;
     for( i = 0+avesize; i &lt;X-avesize ;i++)
       for(j = 0+avesize;j&lt;Y-avesize;j++)
         {
           // loop through sub region of the matrix
           // if the value is not zero add it to the sum
           // and increment the counter. 
           for( int ii = -2; ii &lt; 2; ii ++)
             {
               int iii = i + ii;
               for( int jj = -2; jj &lt; 2 ; jj ++ )
                 {
                   int jjj = j + jj; 
                   tmp_num = gsl_matrix_get(m,iii,jjj); 
                   if(tmp_num != 0 )
                     {
                       summ = summ + tmp_num;
                       total_num++;
                     }
  
  
                 }
             }
           gsl_matrix_set(Matrix_mean,i,j,summ/total_num);
           summ = 0;
           total_num = 0;
  
         }
  </code></pre>
  
  <p>I have some other methods to perform on the 2D array. The one listed is a simple examples.</p>
  
  <p>What I want to do is pass a python 2D array to my c++ function and return a 2D array back to python.</p>
  
  <p>I've read a bit about swig, and have sereached pervious questions, and it seems like it's a possible solution. But I can't seem to figure out what I actually need to do. </p>
  
  <p>Can I get any help? Thanks</p>