My loop returns imaginary results!

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

Thanks in advance

Maryam S.

Answer 1

[madhan ravi]

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]

Thanks Madhan, I see the problem, now I need to replace the NaN values with zero, so I use A(isnan(A)) = 0, but it does not work. Do you think of another solution?

Thanks

Maryam S.

[madhan ravi]

It should work , illustrate for which values it does not work with a simple example.

[Maryam S]

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]

After the loop simply use :

real(A)

[Maryam S]

real(A) does not give me zeros. I used A(imag(A)~=0) = 0 and my problem was solved, thanks to you Madhan!