Multiple loop doesn´t work with right values

Hello, I can´t figure out myself what is wrong with following nested loops:

index = 0;
for i = 1 : 2 : givenValue
    index = index + 1;
    j = i + 1;
    for k = 1 : givenValue/2        
        if sth_x(k) > sth_y(k)
        step(k) = sth_y(k) / sth_x(k);
        end
    end
    for id = 1 : givenValue/2
    values_x{index} = mat(i, 1) : mat(j, 1);
    values_y{index} = mat (i, 2) : step(id) : mat(j, 2);
end

In words, what I need is to generate two cell arrays (values_x and values_y) with one row and several columns, which contains all points (pixels - it is image analysis) between points (pixels) mat(i,1) and mat (j,1) with growing i and j. values_x are allways increased with 1, but values_y are supposed to be increased with step counted before. Problem I have is that cell array values_y is generated with step from the last iteration only. I need values_y{1,1} to be counted with step 1 and values_y{1,2} to be counted with step 2. Therefore values_x{1,1} and values_y{1,1} will be the same length.

I´m new to matlab and I know this might be simple. But I really don´t know what is wrong. I tried to change order of "for" and "if", tried to replace "id" with "k" but still nothing works.

Thank you for your advices very much.

Answer 1

[Nitin]

You might need to initialize your cells first before saving to it.

a = cell(1, num);

[Mariana]

Nitin, thank you for your answer. Unfortunatelly pre-allocating my cell array doesn´t help. I don´t know much about these things but I assumed that pre-allocating increase speed if cycle goes many times. This is cycle ith maximally 6 repetitions. Actually the problem is still the same (even after pre-allocation) - there are two cells in array values_y and they both are counted with the "step" from last iteration. If I write it without cycle with proper numbers it works. When I write in cycle for FIRST column (of matrix mat) it works also. But it doesn´t work when I write it in cycle for second column :( I think there must be some problem of indexing but still can´t figure out what it is :(

[Nitin]

Hopefully this will help, I am not sure what you are trying to achieve though:

index = 0;
 givenValue = 10;
 step = 1:5;
 values_x = cell(1,10);
 values_y = cell(1,10);
 mat= randi(20,20,2);
for i = 1 : 2 : givenValue
    index = index + 1;
    j = i + 1;
    for k = 1 : givenValue/2        
        if 2 > 1
        display('So far so good')
        end
        for id = 1 : givenValue/2
            values_x{index} = mat(i, 1) : mat(j, 1);
            values_y{index} = mat (i, 2) : step(id) : mat(j, 2);
        end
    end
end

For example you can access the elements in the array using values_x{1}

[Mariana]

Thanks for your try :) I copied code into my editor and tried to run it, but it didn´t make me understand how I could solve my problem :( Probably I can ´t explain my problem well via text online. But once again thank you