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# Subscript indices must either be real positive integers or logicals

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RG on 16 Aug 2016
Commented: RG on 17 Aug 2016
Hei All,
I have been getting the error message "Subscript indices must either be real positive integers or logicals. " referring to the calculation of z(i, j) whilst working on the code below. I have spent hours trying to fix the issue, but couldn't figure out what I was missing.
a = 0.2302;
N=4;
theta = linspace(0, 2 * pi * pi, N);
r = linspace(a, 2 * a, N);
sigma_TT = r.^4 .* cos(2 .* theta);
x = zeros(N, N);
y = zeros(N, N);
z = zeros(N, N);
for i = 1:N
for j = 1:N
x(i, j) = (cos(theta(i)))' * r(j);
y(i, j) = (sin(theta(i)))' * r(j);
z(i, j) = real(sigma_TT([theta(i), r(j)]));
end
end
The for loop part is actually what I trying to convert from python to MATLAB. In python it is expressed as:
x = r * np.cos(theta[:,None])
y = r * np.sin(theta[:,None])
z = sigma_TT(SHmax, Shmin, Pp, Pm, a, r, theta[:,None])
Any help on this issue would be much appreciated.
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RG on 17 Aug 2016
You are right, sigma_TT is a separate function. I managed to fix the issue, apparently I forgot to write sigma_TT function. I will post the solution below just for a reference.

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### Accepted Answer

RG on 17 Aug 2016
I had to first create a function called sigma_TT:
function sigma_TT = sigma_TT(r, theta)
sigma_TT = r.^4 .* cos(2 * theta);
The code worked well when sigma_TT is called within compute_sTT function:
function compute_sTT
a = 3;
N = 4;
theta = linspace(0, 3 * pi * pi, N);
r = linspace(a, 3 * a, N);
x = zeros(N, N);
y = zeros(N, N);
z = zeros(N, N);
for i = 1:N
for j = 1:N
x(i, j) = (cos(theta(i)))' * r(j);
y(i, j) = (sin(theta(i)))' * r(j);
z(i, j) = sigma_TT(r(j), theta(i));
end
end
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### More Answers (1)

Image Analyst on 16 Aug 2016
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RG on 17 Aug 2016
Yes, it was useful indeed. Many thanks for it.

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