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st: RE: Re: RE: summing up matrix elements


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Re: RE: summing up matrix elements
Date   Tue, 8 Nov 2005 17:59:30 -0000

You may be thinking of Jeroen Weesie's -matsum-. 
Offhand, I can't think of any reason why anyone 
with Stata 9 would prefer that. Nor, I imagine, 
would Jeroen if he were to be asked. 

STB-39  dm49  . . . . . . . . . . . . . . . . . . . . Some new matrix commands
        (help matfunc, varfunc if installed)  . . . . . . . . . . .  J. Weesie
        9/97    pp.17--20; STB Reprints Vol 7, pp.43--48
        collection of new matrix commands; several for explicit matrices
        and a few for implicit matrices (i.e., variables)

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

R.E. De Hoyos
 
> Both your solutions work fine, thanks a lot. 
> I though there was a non-mata matrix function similar to 
> mata's -sum(C)-

Nick Cox

. mata : sum_r = (sum(C) - trace(C)) / 2

R.E. De Hoyos

> >> > Is there a way to to get a scalar containing the sum of the 
> >> > off-diagonal 
> >> > elements of a pre-defined matrix?
> >> > 
> >> > For instance, define matrix C  as a correlation matrix. I 
> >> > want to know what 
> >> > is the sum of correlations between the various elements in C. 
> >> > Therefore I 
> >> > need the sum of all elements in C minus the sum of the 
> >> > diagonal elements 
> >> > (-trace(C)-) and finally divide it by 2 (I am assuming 
> matric C is 
> >> > symetric).

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