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st: RE: Matrix calculation


From   "Steichen, Thomas" <STEICHT@RJRT.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Matrix calculation
Date   Fri, 6 Sep 2002 16:24:23 -0400

I believe the problem is that syminv(A) requires that A be 
positive definite to generate a normal inverse. Your A is 
not positive definite, so syminv(A) returns a g2 inverse.


> -----Original Message-----
> From: Jiang, Tao [mailto:TJiang@air.org] 
> Sent: Friday, September 06, 2002 3:57 PM
> To: 'statalist@hsphsun2.harvard.edu'
> Subject: st: Matrix calculation
> 
> 
> I was doing some matrices calculation, but got some problem.  
> What I had is
> a simple matrix:
> 
> A = (1,2\2,1)
> 
> and if I do B = inv(A), I got the correct matrix; if I do B = 
> syminv(A),
> I got the following:
> 
> . mat A = (1,2\2,1)
> . mat list A
> 
> symmetric A[2,2]
>     c1  c2
> r1   1
> r2   2   1
> . mat iA=syminv(A)
> 
> . mat list iA
> 
> symmetric iA[2,2]
>     r1  r2
> c1   1
> c2   0   0
> 
> Is there some reason why?
> *
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> 
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