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Asked by Cruise on 30 Nov 2011

I have a mathematical function.This's a numeric string. How can i calculate sum of numeric string? Example: Sum of (1/3^n) with n from n to extend at infinity And what is symbol of infinity in matlab? Thanks.

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Answer by Naz on 30 Nov 2011

I hope you realize that computer has finite memory and can not run it forever to reach your infinity, so you gonna have to stop somewhere :). Here's what you can do:

yoursum=0; y='1/3^n'; f=inline(y);

for x=1:1000 yoursum=yoursum+f(x); end yoursum

Answer by Walter Roberson on 30 Nov 2011

If you have the symbolic toolbox,

syms n symsum(sym('1/3')^n, n, n, inf)

Please, though, recheck that your lower bound is really "n" just like the variable of summation. Using the same variable in both places can lead to some odd calculations. Did you perhaps mean that n should be from 1 to infinity? If so then put 1 in place of the parameter that is before infinity (the lower bound of the summation.)

Cruise on 30 Nov 2011

This is a convergent series and i want to use convergent characteristic to calculate sumation.

syms x k

s1 = symsum(1/k^2,1,inf)

s2 = symsum(x^k,k,0,inf)

when i type this code in command window.why matlab don't show me "s1"?

Walter Roberson on 30 Nov 2011

I do not know why that code would not show s1 . Unfortunately I cannot test it myself.

You could try

s1 = symsum(1/k^2,k,1,inf)

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