How to make a serie ?
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Hi, i need to write a sum of serie :
with b_k= (k+1)^2-(k)^2 and u^(m-k) is the numerical solution approximation u(x,t_m-k) for k=1,...m-1 and m=1,....,20
for m=1:20
syms k u
b(k)=(k+1)^2-k^2;
F=symsum((b(k)-b(k+1))*u(:,m-k),k,1,m-1)
end
F
but i get error
Necessary I need u(:,m-k)
Please help me
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Walter Roberson
2020년 12월 16일
It is never possible to use a symbolic variable as an index in MATLAB.
You need to create a definite list of values and sum() the list. Or loop adding on to a total.
Note by the way that and so b(k) - b(k+1) = (2*k+1) - (2*(k+1)+1) = -2
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Walter Roberson
2020년 12월 17일
Sorry, you are changing equations too much. Your equation here is quite different than your equation in your Question, and it is not really reasonable to answer both at the same time as they are too different. What is the question you need answered?
Note: using U(:,m-k) is not equivalent to as t is obviously a vector of values that as outside observers we need to assume is a real number in ℝ or possibly even in ℂ and cannot assume that t just happens to be linear indices . At the very least it is likely that t starts from 0, and so is not suitable for indexing. Indeed, since then k can equal m, and then would be 0, and that is not a valid matrix index.
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