Why do I get 'Array indices must be positive or logical values' in symsum function?

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C Ma 2023-3-18

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https://ww2.mathworks.cn/matlabcentral/answers/1931210-why-do-i-get-array-indices-must-be-positive-or-logical-values-in-symsum-function

评论： Matt J 2023-3-19

syms n
h=0.05;
U=0.02;
delta_t=1;
v=1.846*10^-5;
d=1.117;
t=50;
y=0.2;
P=pi;
F=symsum((1/n)*exp(-((n^2)*(P^2)*v*t)/(d*(h^2)))*sin(n*P(1-y/h)),n,1,300);
Array indices must be positive integers or logical values.
u=U*y/h-(2*U/P)*F(n);

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Torsten 2023-3-19

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移动：Torsten 2023-3-19

在 MATLAB Online 中打开

h=0.05;
U=0.02;
delta_t=1;
v=1.846*10^-5;
d=1.117;
t=50;
y=0.2;
P=pi;
n = 1:300;
Fn = 1./n.*exp(-(n.^2*P^2*v*t)/(d*h^2)).*sin(n*P*(1-y/h));
F = cumsum(Fn);
u=U*y/h-(2*U/P)*F;

更多回答（1 个）

Matt J 2023-3-18

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1931210-why-do-i-get-array-indices-must-be-positive-or-logical-values-in-symsum-function#answer_1195980

编辑：Matt J 2023-3-19

在 MATLAB Online 中打开

The error is because you appear to be indexing P with a non-integer. Did you mean to write,

sin(n*P*(1-y/h))

So basically I want to get the summation of F values by substituting n from 1 to 300 into this equation. F(n) is an array storing values with indices n=[1:300]. For example, F(3)=Fsum(1)+Fsum(2)+Fsum(3), F(2)=Fsum(1)+Fsum(2).

Matt J 2023-3-19

Torsten's answer should give that to you, but in the meantime, since I have answered your posted question, please Accept-click the answer and, if Torsten's response doesn't get you where you need, post a new question.

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