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st: RE: RE: Sum product of each element with each other element except itself?


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: Sum product of each element with each other element except itself?
Date   Sun, 16 Aug 2009 16:52:59 +0100

It sounds as if you just keep going, using the principle that sum of
(everything - somethings) = sum(everything) - sum(somethings). 

Nick 
n.j.cox@durham.ac.uk 

Martin Weiss

This FAQ may be helpful:
http://www.stata.com/support/faqs/data/members.html

Apart from that, give an excerpt of your data, and show exactly what you
want to happen to it...

Stata Chris

I would like to compute the following in Stata:

Sum over all n of:  Sum over all m unequal n of:
(D_nt - p)*(D_mt - p),

where m, n, t are subindices.

If it was with only a single sum and without the unequal condition, I
would just have used sth like this:
bysort m n t:  gen factor1 = (D_nt - p)
bysort m n t:  gen factor2 = (D_mt - p)
bysort t:        egen result = sum(factor1*factor2)

But I'm not sure how to get the product for each element n with each
other element from the same set except itself.
Should I do this with a loop or sth?

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