Subscript indices must either be real positive integers or logicals

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RG 2016-8-16

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评论： RG 2016-8-17

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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Ammar Dodin 2016-8-16

编辑：Ammar Dodin 2016-8-16

I am not too familiar with numpy, but I think I understand what the first two lines of your python code are doing. It looks like you're creating new vectors that contain the cosine/sin of each of the values of the vector theta after multiplying them with some constant. I don't understand what z is doing? I am assuming sigma_TT is some function you wrote.

Could you possibly provide the Python code for that function?

RG 2016-8-17

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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Answer 1

RG 2016-8-17

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/299784-subscript-indices-must-either-be-real-positive-integers-or-logicals#answer_232061

在 MATLAB Online 中打开

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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Answer 2

Image Analyst 2016-8-16

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/299784-subscript-indices-must-either-be-real-positive-integers-or-logicals#answer_231938

It's pretty well explained in the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_fix_the_error_.22Subscript_indices_must_either_be_real_positive_integers_or_logicals..22.3F

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Image Analyst 2016-8-17

I thought my comment would explain it more thoroughly than his original 2-line comment. Anyway, hopefully you looked over the FAQ and maybe found some other good stuff in there.

RG 2016-8-17