Acessing numerical matrix in symsum function

Question

Bruno Tondin 2018-4-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/397873-acessing-numerical-matrix-in-symsum-function

回答： Walter Roberson 2018-4-28

采纳的回答： Walter Roberson

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Hello,

I'm having some trouble trying to run this code

clc;
clear;
close all
%%Imagem
IM = [1 2 3; 4 5 6; 7 8 9]
im = sqrt(-1);
%%Data
ind = 3;
omeg = 2^(-((ind+2)/2));
sig = (2*pi^2)/omeg;
thet = 0;
%%first
% J = sum(0,k)[f(k,y) H(x - k) S(x-k)
y = 0;
syms k x
%soma = IM(y+1,k+1)*exp(im*omeg*sin(thet))*exp(-0.5*((x-k)/sig)^2);
J0 = symsum(IM(y+1,k+1)*exp(im*omeg*sin(thet))*exp(-0.5*((x-k)/sig)^2), k, 0, 3)

I got the following error:

Error using sym/subsindex (line 766) Invalid indexing or function definition. When defining a function, ensure that the arguments are symbolic variables and the body of the function is a SYM expression. When indexing, the input must be numeric, logical, or ':'.

How can I get values from a numeric matrix in symbolic sum?

Thank you

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Answer 1

Walter Roberson 2018-4-28

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/397873-acessing-numerical-matrix-in-symsum-function#answer_317638

It is never valid to index an array at a symbolic variable.

Instead, if you have fixed endpoints, generate a vector of the values over the range, and the sum() the vector.

symsum() is for finding closed form formulas for summations, not for adding definite terms. For example if you were to pass the taylor expansion for sin(x) to symsum then it would be able to recover sin(x).