But when col 1 is less than col 2, you're still replacing it. Just look at your third row. Please make your explanation match your example. You just simply replaced column 3 with column 1 regardless of what column 2 is.
Perhaps you mean this:
m = [5,4,0; 3,1,0; 5,7,0]
% Assign column 1 to column 3
% but only when it's greater than column 2
rowsToReplace = m(:, 1) > m(:, 2)
m(rowsToReplace, 3) = m(rowsToReplace, 1)
