# Trying to code a tricky double summation

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Michael Vaughan 2020년 9월 24일
댓글: Ameer Hamza 2020년 9월 24일
So I'm trying to write code that calculates the following:
I have two functions of the same two variables, call them D(x,y) and T(x,y)
I'm trying to write a function that accepts inputs x,y,z and outputs: So, there are two summations, the outer one takes the sum from i=0 up to min(x,y), and the inner sum takes the summation of terms from k=0 up to x-i
The inner sum isn't as complicated as it looks, it has a (-1)^k at the start and then just multiples the functions D(a,b) and T(a,b)^(z/2) where a and b depend on both where you are in the indexing of your outer summation and inner summation
This is a much harder proram than I have written before, so tips, insights, general advice, and even completed code are welcome!! Thanks for your time

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### 채택된 답변

Ameer Hamza 2020년 9월 24일
Something like this should work
s = 0;
for i=0:min(x,y)
for k=0:x-1
s = s + (-1)^k * D(2*x-2*k-2*i, 2*y+2-2*i) * T(2*x-2*k-2*i, 2*y+2-2*i)^(z/2)
end
end
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Ameer Hamza 2020년 9월 24일
To make a function handle type this
S1 = @Sum1
S1(3,2,1)

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