Re: help on calculating sum of combinations

[Mike Miller]

On Wed, 8 Oct 2003, Miquel Cabanas wrote:

> >       a2=2*3+2*4+2*5
>
> that's easy too, take the first element of A, i.e. "A(1)", and
> multiply it element-by-element, i.e. ".*", by all remaining elements
> of A, that is from A(2) to A(length(A)), i.e. "A(2:length(A))"

For the sum of products of all pairs of elements of column vector A, you
can do this:

a2 = sum(tril(A*A',-1))

If A is a row vector, you have to do this instead:

a2 = sum(tril(A'*A,-1))

Mike



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