# My loop returns imaginary results!

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Maryam S on 30 May 2020
Commented: Maryam S on 30 May 2020
Hello,
I write this simple code in a loop, and I obtain unwabted imaginary results. Could you please tell me where my mistake is:
SO = 0.5 .* ones(10,1);
A(1,:) = 5.02 * (16.6 / 42) ^ 0.33 * SO(1,:) ^ 0.38;
for i = 2 : 10
A(i,:) = 5.02 * ((16.6 - sum(A(1:i-1,:)))/ 42) ^ 0.33 * SO(i,:) ^ 0.38;
end
Maryam S.

madhan ravi on 30 May 2020
Edited: madhan ravi on 30 May 2020
Evaluate the part
((16.6 - sum(A(1:i-1,:)))/ 42)
and see what happens when the sum(...) is greater than 16.6
Note: No loop needed here sum(...) could be replaced by cumsum(...) and linear indexing is sufficient, subscript indexing is not needed here since it’s a vector.

Maryam S on 30 May 2020
from A(7,:) the 16.6 - sum(A(1:i-1,:) gets negative and the resluts get imaginary. But how to replace the imaginary resuts with zero?
madhan ravi on 30 May 2020
After the loop simply use :
real(A)
Maryam S on 30 May 2020
real(A) does not give me zeros. I used A(imag(A)~=0) = 0 and my problem was solved, thanks to you Madhan!