CODEWITHSUNDEEP
gams-math
user3917718
user3917718

Reputation: 105

How to filter elements with identical indices in GAMS?

I have a GAMS model where I have

 Set   i       / 1*6 /;
 Alias (i,ip,il) ;
 Variables
  x(i,ip) ;

And I want to generate equations which operates on the scalar products of all vectors in x, excluding the product of the same vector. Something like:

 scalarProduct(i)..
  sum(ip,x(i,ip)x(i,il)) =e= someConstant;

However this does not exclude the product of identical vectors. How to add this? Can I do it with a dollar statement somehow? There's probably a few bugs in that statement anyway, I didn't try it because I think the exclusion I want is missing.

Upvotes: 1

Views: 414

Answers (1)

user3917718
user3917718

Reputation: 105

so what I wanted to do is this: 

Sets
i        / 1*13 /
ii(i,i) diagonal elements / #i:#i /
ij(i,i) all elements / #i.#i /
ij_wo_ii(i,i);

get all combinations without the diagonal elements:

ij_wo_ii(i,j) = ij(i,j) - ii(i,j);

and then I use it in an equation like this:

equation(j,k)..
  sum(i,x(i,j)*x(i,k)$ij_wo_ii(j,k)) =l= 1;

This does something similar to orthogonality, except that the product of vectors in a matrix must be smaller than some value and not necessarily 0. don't know if there is a term for this. Hope it will be of use to someone else as well.

Upvotes: 1

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