# Need help programming a few tricky calculations!!

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Michael Vaughan on 26 Sep 2020
Commented: Alan Stevens on 26 Sep 2020
Can somebody show me how to write a program to calculate a program that you input and N and the output is: thank you
edit: in regualer text rather than attempt to write latex:
f(n) = [ ( (-1)^(n-1)*t^(2-2n) ) / ( 1-t^(-4) ) ] sum_k=0^{n-1} t^-4nk product_{i=0}^k (1-t^(4i-4n))

Alan Stevens on 26 Sep 2020
Here is one way to do the function, assuming you are looking for a numerical output, and that you pass it t as well as n:
n = ... % choose your number
t = ... % ditto
output = fn(n,t);
function f = fn(n,t)
c = (-1)^(n-1)*t^(2-2*n)/(1-t^-4);
S = 0;
for k = 0:n-1
tm = t^(-4*n*k);
P = 1;
for i = 0:k
P = P*(1-t^(4*i-4*n));
end
S = S + tm*P;
end
f = c*S;
end

Michael Vaughan on 26 Sep 2020
Thank you. SO would I put this in a script named fn ?? Would the script start with output ??
Alan Stevens on 26 Sep 2020
You would have to give the script a different name, not fn. These sorts of functions (like fn) always come at the end of the script.