On Thu, 18 Oct 2001, Trenkler, Dietrich wrote:
> Thorsten is right. There is a direct formula for computing the
Moore-Penrose
> inverse
> using the singular value composition of a matrix. This is incorporated in
> the following:
>
> mpinv <- function(A, eps = 1e-13) {
> s <- svd(A)
> e <- s$d
> e[e > eps] <- 1/e[e > eps]
> return(s$v %*% diag(e) %*% t(s$u))
> }
>
> Hope it helps.
That's what ginv in library MASS already does, except that it uses a
relative tolerance (yours will fail for a matrix of the order of
10^(-20)), handles the complex case, the rank 1 case, .... In short, it
has been proven over a decade. It's by the other author of MASS, BTW.
>
> > -----Ursprüngliche Nachricht-----
> > Von: Torsten Hothorn
> > Gesendet am: Thursday, October 18, 2001 9:52 AM
> > An: Philippe Grosjean
> > Cc: r-help at stat.math.ethz.ch
> > Betreff: RE: [R] General Matrix Inverse
> >
> >
> >
> > > I use solve(x) to find the inverse of a matrix (don't know
what a
> > "general
> > > inverse" is). By the way, what is better: solve(x),
qr.solve(x) or
> > ginv(x)?
> > > ginv(x) seems to give results for matrices where solve and
qr.solve
> > return
> > > an error:
> > >
> > > > x <- matrix(1:9, 3, 3)
> > > > x
> > > [,1] [,2] [,3]
> > > [1,] 1 4 7
> > > [2,] 2 5 8
> > > [3,] 3 6 9
> > > > solve(x)
> > > Error in solve.default(x) : singular matrix `x' in solve
> > > > qr.solve(x)
> > > Error in qr.solve(x) : singular matrix `x' in solve
> > > > ginv(x)
> > > [,1] [,2] [,3]
> > > [1,] -0.6388889 -5.555556e-02 0.5277778
> > > [2,] -0.1666667 4.163336e-17 0.1666667
> > > [3,] 0.3055556 5.555556e-02 -0.1944444
> > >
> >
> > if A is singular, A^-1 is not defined but a generalized inverse G is,
> > namely
> >
> > G is generalized inverse of A <=>
> >
> > A G A = A (sometimes G is written as A^-)
> >
> > G is not unique, but adding 3 conditions
> >
> > - G A G = G
> >
> > - t(G A) = G A
> >
> > - t(A G) = A G
> >
> > makes G unique (Moore-Penrose-Inverse)
> >
> > Torsten
> >
> >
> > > Regards,
> > >
> > > Philippe Grosjean
> > >
> > >
> > >
...........]<(({?<...............<?}))><...............................
> > > ) ) ) ) ) __ __
> > > ( ( ( ( ( |__) | _
> > > ) ) ) ) ) | hilippe |__)rosjean
> > > ( ( ( ( ( Marine Biol. Lab., ULB, Belgium
> > > ) ) ) ) ) __
> > > ( ( ( ( ( |\ /| |__)
> > > ) ) ) ) ) | \/ |ariculture & |__)iostatistics
> > > ( ( ( ( (
> > > ) ) ) ) ) e-mail: phgrosje at ulb.ac.be or phgrosjean at
sciviews.org
> > > ( ( ( ( ( SciViews project coordinator (http://www.sciviews.org)
> > > ) ) ) ) ) tel: 00-32-2-650.29.70 (lab), 00-32-2-673.31.33
(home)
> > > ( ( ( ( (
> > > ) ) ) ) ) "I'm 100% confident that p is between 0
and 1"
> > > ( ( ( ( ( L. Gonick & W.
Smith (1993)
> > > ) ) ) ) )
> > >
.......................................................................
> > >
> > >
> > > -----Message d'origine-----
> > > De : owner-r-help at stat.math.ethz.ch
> > > [mailto:owner-r-help at stat.math.ethz.ch]De la part de Prof
Brian Ripley
> > > Envoye : jeudi 18 octobre 2001 04:25
> > > A : Randall Skelton
> > > Cc : r-help at stat.math.ethz.ch
> > > Objet : Re: [R] General Matrix Inverse
> > >
> > >
> > > On Wed, 17 Oct 2001, Randall Skelton wrote:
> > >
> > > > What is the easiest (not the fastest) way to find the
general inverse
> > of a
> > > > matrix in R?
> > >
> > > If you mean the generalized inverse, ginv() in package MASS.
Otherwise,
> > > pleae tell us what a `general inverse' is.
> > >
> > >
> > > --
> > > Brian D. Ripley, ripley at stats.ox.ac.uk
> > > Professor of Applied Statistics,
http://www.stats.ox.ac.uk/~ripley/
> > > University of Oxford, Tel: +44 1865 272861 (self)
> > > 1 South Parks Road, +44 1865 272860 (secr)
> > > Oxford OX1 3TG, UK Fax: +44 1865 272595
> > >
> > >
> >
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--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272860 (secr)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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