# Skipping even indices in a for-loop and subsequently avoiding the odd values to appear in the output

4 views (last 30 days)
NN on 15 Apr 2019
Answered: Dennis on 15 Apr 2019
Through a nested-for-loop for n=1 and m=1,3 i want to acquire a matrix A with elements a1 and a2
m_length = 3;
n_length = 1;
for n=1:1:n_length
for m=1:2:m_length
a1(n,m) = ((n-1)+m);
a2(n,m) = ((n-1)+m);
end
end
A = [a1 a2];
The above would output A as
A = [1,0,3,1,0,3]
It takes into account the even values of m too (and equates them to 0).
But what i require is purely the odd values of m (i.e. m=1,3) in the matrix.
What i would like to see is:
A = [1,3,1,3]
PS: In the original problem, n = 0,1,2,3,4...n_length and m = 1,3,5,7,9...m_length.
I shortened m and n and their total lengths for ease of explaining the problem.

Dennis on 15 Apr 2019
When you assign a value to A(3,3)=1, Matlab will create a Matrix of the size 3,3 and will fill empty fields with 0.
A(3,3)=1
A =
0 0 0
0 0 0
0 0 1
This is what is happening in your code. One possible solution might be to fix the index of your matrix:
m_length = 3;
n_length = 1;
for n=1:1:n_length
for m=1:2:m_length
a1(n,(m+1)/2) = ((n-1)+m);
a2(n,(m+1)/2) = ((n-1)+m);
end
end
A = [a1 a2];