# Multiple loop doesn´t work with right values

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Mariana on 18 Mar 2014
Commented: Mariana on 19 Mar 2014
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.

Nitin on 18 Mar 2014
You might need to initialize your cells first before saving to it.
a = cell(1, num);

Mariana on 19 Mar 2014
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 on 19 Mar 2014
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 on 19 Mar 2014
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