I used to add the matrix to itself and
Then multiply by 0.5 or something
Like that but I don't recall exactly.
Someone else may remember the details.
All I remember is that it worked
For symmetry problems with Splus. Maybe
Finmetrics is different though.
mark
-----Original Message-----
From: s-news-owner@lists.biostat.wustl.edu
[mailto:s-news-owner@lists.biostat.wustl.edu] On Behalf Of Eric Gravengaard
Sent: Monday, April 19, 2004 4:22 PM
To: Stahel, Christof
Cc: s-news@lists.biostat.wustl.edu
Subject: Re: [S] chol error in Finmetric's SUR
Christof,
I've had similar errors when using a Choleski decomposition. It comes down to
the matrix not being symmetric. The problems usually arise when the matrix is
symmetric, but because of machine precision limitations doesn't look symmetric
to a machine. I do not have a work around except to use Matlab to do this
because their implementation does not have this limitation.
Do others have work arounds or possibly another implementation of the Choleski
decomposition that would help to solve this problem?
-Eric
On Sat, 17 Apr 2004 12:49:12 -0400, Stahel, Christof <stahel_2@cob.osu.edu>
wrote:
>
> Dear all,
> I receive the following error
>
> Problem in chol(xpx[X.idx[[i]], X.idx[[i]]]): Matrix must be symmetric
> Use traceback() to see the call stack when I call SUR in Finmetrics
> using the sample code straight from the help file. Any idea what
> causes the problem?
>
> # simulate a multivariate data set.
> set.seed(10)
> x1 <- abs(rnorm(100))
> x2 <- x1^2
> sim.dat <- data.frame(x1=x1,
> x2=x2,
> y1=1+2*x1+rnorm(100),
> y2=4+5*x2+rnorm(100))
> # estimate an SUR model
> SUR(list(y1~x1, y2~x2), data=sim.dat)
>
> I am using release 6.0.2 for windows on a 3.06 Pentium 4 HT running
> XP.
>
> Thanks VERY much for your help & input!
> C
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