for loop - Array indexing problem

I'm working on a program, and one part of it can be seen below. I need the for loop to start at i = 1 and j = 2 only for the x variable but still run trough points like (i=2,j=1)(So obviously adding +1 to j doesn't work). Do you have any ideas how that is possible? Note, point (i=1,j=1) has to be valid for z and y. Thanks in advance!

for i = 1:10
    for j = 1:12
       if x(i,j) > y(i,j)         
            z(i,j) = y(i,j) - x(i,j)
       else            
            z(i,j) = x(i,j) / x(1,1)
       end
    end
end

Answer 1

[Robert U]

Hi Arnar Þór Ólafsson,

you can use any vector to run for-loops. You can assign the values in the order as you wish. It might be necessary to preallocate the result matrix in order to avoid errors assigning elements that do not exist, yet.

Result = zeros(3);
indRow = [2 3 1];
indCol = [2 1 3];

ind = 1;
for ik = indRow
    for jk = indCol
        Result(ik,jk) = ind;
        ind = ind + 1;
    end
end

You can use index-pairs (row & column) or single index. You can even convert between these two index descriptions.

• for loop
• array indexing
• ind2sub - convert linear indices to subscripts
• sub2ind - convert subscripts to linear indices

Kind regards,

Robert