# Issues using Summation in Matlab

3 views (last 30 days)
Matthew Charles on 6 Jul 2022
Commented: Matthew Charles on 6 Jul 2022
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: Chunru on 6 Jul 2022
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
Matthew Charles on 6 Jul 2022
Thanks @Chunru duly noted. I will make the necessary adjustments

Walter Roberson on 6 Jul 2022
Edited: Walter Roberson on 6 Jul 2022
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
Matthew Charles on 6 Jul 2022
Okay not a problem, thank you very much

R2022a

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