# [R] General Matrix Inverse

Philippe Grosjean phgrosje at ulb.ac.be
Thu Oct 18 09:11:54 CEST 2001

```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

Regards,

Philippe Grosjean

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-----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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