Issues using Summation in Matlab

Question

Matthew Charles 2022-7-6

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评论： Matthew Charles 2022-7-6

Hi, just want to confirm whether the code that I have below is indeed correct or there are changes that is needed to solve. I have values of "n' and "d" that I have to input but the summation tool id new to me

syms i n d

SMD = symsum(n*d^3/(n*d^2),i,1,N)

formula:

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Answer 1

Chunru 2022-7-6

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This is symbolic computation. It's not clear what you want to calculate exactly.

If you have value of d and n, you may want to do numerical summation. For example

d = [1 3 4 2];
n = [2 5 6 7];
% sum first, then division
s1 = sum(d)/(sum(n))
s1 = 0.5000
% division first, then sum
s2 = sum(d./n)
s2 = 2.0524

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Matthew Charles 2022-7-6

Thanks @Chunru duly noted. I will make the necessary adjustments

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Answer 2

Walter Roberson 2022-7-6

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https://ww2.mathworks.cn/matlabcentral/answers/1754255-issues-using-summation-in-matlab#answer_1001060

编辑：Walter Roberson 2022-7-6

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never use symsum to form the sum of a vector of values. The variable of summation for symsum is always symbolic, but symbolic values can never be used to index anything.

symsum should only be used when you are working with formulas, such as

symsum((-1)^n / 2^n, n, 1, m)

hoping to get out a function like (-1/2)^m/3 - 1/3