Let's say
A = [1 2 3; 4 5 6; 7 8 9];
[row,columns] = size(A); index_matrix = zeros(1,columns)
for i = 1:columns
[large,index] = max(:,i);
index_matrix(i) = index;
end
%The index_matrix vector should store the position of the max value of each column
