Array indices must be positive integers or logical values

Question

Aneesa Shahbaz 2021-4-12

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/799826-array-indices-must-be-positive-integers-or-logical-values

评论： Aneesa Shahbaz 2021-4-14

采纳的回答： Daniel Pollard

U0 = 0.1;

V0 = 0.5;

W = 1;

t = 1;

x = linspace(0,3); % create linear spacing in x-direction

y = linspace(0,3); % create linear spacing in y-direction

XX = zeros(length(x),length(y));

YY = zeros(length(x),length(y));

%looping in i and j-directions

for i = 1:length(x)

for j = 1:length(y)

%create x & y space

XX(i,j) = x(i);

YY(i,j) = y(j);

psi(i,j) = ((U0*V0)./W)*cos(W(t-YY(i,j)./V0))-V0*XX(i,j);

I get an error message of

Array indices must be positive integers or logical values.

Error in psi(i,j) = ((U0*V0)./W)*cos(W(t-YY(i,j)./V0))-V0*XX(i,j);

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Answer 1

Daniel Pollard 2021-4-12

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/799826-array-indices-must-be-positive-integers-or-logical-values#answer_673296

在 MATLAB Online 中打开

You wrote

psi(i,j) = ((U0*V0)./W)*cos(W(t-YY(i,j)./V0))-V0*XX(i,j);

Try

psi(i,j) = ((U0*V0)./W)*cos(W*(t-YY(i,j)./V0))-V0*XX(i,j);

W is not a vector or matrix, so calling W(t-YY(i,j)./V0) won't return anything sensible. I think you mean to multiply W by the bracketed term in the cos.

Side note: i and j make terrible variable names in Matlab. They already have a built in value of the complex unit, so redefining that is likely to throw errors further down the line. I tend to use ii, jj or k for loop indices to avoid this problem.