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

 From "Martin Weiss" To Subject st: RE: Sum product of each element with each other element except itself? Date Sun, 16 Aug 2009 12:26:03 +0200

```<>

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...

HTH
Martin

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Stata Chris
Sent: Sonntag, 16. August 2009 01:19
To: statalist@hsphsun2.harvard.edu
Subject: st: Sum product of each element with each other element except
itself?

Hi,

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?

Many thanks,
Chris
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/
```