Finding change in direction

I would like to check all neighbor elements for every element in a 600x400 matrix for a change in direction

for i=1:size(gx,1)
    for j=1:size(gx,2)
        el_1=matrix(i,j) % Give the value of present element having position i,j
        el_2=matrix(i,j-1) % Left element
        el_3=matrix(i,j+1) % Right element
        el_4=matrix(i-1,j) % for upper element 
        el_5=matrix(i+1,j)%Upper element
        el_6=matrix(i-1,j-1) % West-North Diagonal Element....
        if el_1*el_2<0
            .....
        end 
    end 

I thought of checking each element

[KSSV]

REad about gradient.

Answer 1

[Bruno Luong]

Your code will crash since indexing will be overflowed.

Just an idea you might do the sign comparison of the entire array

[r,c] = find(matrix(:,1:end-1) .* matrix(:,2:end) < 0);
...

The use r, c to do whatever you want to do next.