creating a max-pooling layer using nested loop.

I am trying to make a max pooling layer with a 3x3 filter and stride 3. I'm trying to only use for loops for this code to work. here is my code.

main = [1 2 3 4 5 6;
        7 8 9 10 11 12;
        13 14 15 16 17 18;
        19 20 21 22 23 24;
        25 26 27 28 29 30;
        31 32 33 34 35 36];
temp=0;
%temporary var for stride
tmpX=0;
tmpY=0;
 for x=1:size(main,1)/3
     for y=1:size(main,2)/3
         for cx=1:3
             for cy=1:3
                 %stride by 3
                 cy = cy+tmpY;
                 cx = cx+tmpX;
                 if main(cx,cy)>temp
                     temp = main(cx,cy)
                 end
             end
         end
         if y == size(main,2)/3
             tmpY=0;
             tmpX=tmpX+3;
         else
            tmpY=tmpY+3;
         end
     end
 end

I'm using the matrix 'main' as a sample input for the pooling, the program should give a 2x2 matrix output of [15,18,33,36] but I'm getting [15,18,19,0] ad an error message that says 'Index in position 1 exceeds array bounds (must not exceed 6).'

Answer 1

[Image Analyst]

Just look at what the variables are. cx is 7 and main is only 6 wide.

By the way, matrices have the horizontal (column) index second, not first like you have it. So matrices are main(y, x) NOT main(x, y).