[R] Matrix Inversion

[Robin Hankin]

Hello Wang

matrix bb is symmetric positive semidefinite, so
algebraically the eigenvalues are nonnegative.

I would use

bb <- crossprod(b)

to calculate bb (faster and possibly more accurate)

Look at eigen(bb,TRUE,TRUE)$values

(see ?eigen for the meaning of the arguments) to see how
many very small eigenvalues you have.  The number of zero
eigenvalues is equal to the number of linear relations
in the columns of b.


HTH


rksh



On 12 Dec 2007, at 10:59, Wang Chengbin wrote:

> I got the following error:
>
> a = read.csv("mat.csv")
> b = as.matrix(a)
> tb = t(b)
> bb = tb %*% b
> dim(bb)
> ibb = solve(bb)
> bb %*% ibb
>
>> ibb = solve(bb)
> Error in solve.default(bb) :
>   system is computationally singular: reciprocal condition number =
> 1.77573e-19
>>
> Are there any ways to find more information about why it is singular?
>
> Thanks.
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--
Robin Hankin
Uncertainty Analyst and Neutral Theorist,
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
  tel  023-8059-7743