how does sum work?

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Pavel Kuzmitsky
Pavel Kuzmitsky on 22 Nov 2020
Edited: Walter Roberson on 23 Nov 2020
I don't understand what I'm doing wrong, it should be -1, but it turns out -0.5
but if you calculate separately for s=0 and s=1 and add it up, it turns out that -1 is true
clear
clc
n=2;
m=0;
k=(n-m)/2;
q=(n+m)/2;
r2=0;
s=0:k;
R=sum((r2.^(n-(2.*(s)))).*...
(((-1).^(s)).*(factorial(n-(s))))/...
((factorial(s)).*(factorial(q-(s))).*(factorial(k-(s)))))
also, if you can explain how to improve the formula so that it can be used when
r2=linspace(0,1,500);
if you can, write comments on actions in the response so that it is clear how your code works

Accepted Answer

Walter Roberson
Walter Roberson on 23 Nov 2020
you have one / operator that should be ./
  3 Comments
James Tursa
James Tursa on 23 Nov 2020
(((-1).^(s)).*(factorial(n-(s))))/... <-- that one
Walter Roberson
Walter Roberson on 23 Nov 2020
Edited: Walter Roberson on 23 Nov 2020
n = 6;
m=0;
k=(n-m)/2;
q=(n+m)/2;
r2 = linspace(0,1,25);
s = (0:k).';
R = sum((r2.^(n-(2.*(s)))) .* ...
(((-1).^(s)).*(factorial(n-(s)))) ./ ...
((factorial(s)).*(factorial(q-(s))).*(factorial(k-(s)))));
size(R)
ans = 1×2
1 25
plot(r2, R);
xlabel('r2'); ylabel('R');

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