[R] What does the command diag(solve(matrix)) do?

[Peter Alspach]

Tena koe Tiago

?solve
?diag

will tell you what those R functions do.  Why the code wants the diagonal of the inverse of that particular correlation matrix is another matter.  If the matrix is the so-called numerator relationship matrix (i.e., twice the coancestry matrix) then its inverse is used in fitting the so-called animal model.  See Lynch, M. and B. Walsh (1998)  Genetics and Analysis of Quantitative Traits. Sunderland, MA, USA,  Sinauer Associates, Inc. in particular chapters 26 and 27 (I think) for more details.

HTH ....

Peter Alspach

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of tiago.pereira at mbe.bio.br
> Sent: Wednesday, 13 April 2011 12:44 p.m.
> To: r-help at r-project.org
> Subject: [R] What does the command diag(solve(matrix)) do?
> 
> Hello, R users!
> 
> As a geneticist, and new user of R are still find some basic questions
> hard
> to solve. For example, I am trying to understand a code, which uses,
> for
> instance, a matrix of correlations:
> 
> >mymatrix
> [,1]      [,2]      [,3]      [,4]      [,5]
> [1,] 1.0000000 0.2500000 0.2357023 0.2182179 0.2721655
> [2,] 0.2500000 1.0000000 0.3535534 0.3273268 0.4082483
> [3,] 0.2357023 0.3535534 1.0000000 0.3086067 0.3849002
> [4,] 0.2182179 0.3273268 0.3086067 1.0000000 0.3563483
> [5,] 0.2721655 0.4082483 0.3849002 0.3563483 1.0000000
> 
> So far, so good. I understand well what this matrix means. Then, the
> following line shows up:
> 
> 
>  solved<- diag(solve(mymatrix))
> 
> > solved
> [1] 1.131429 1.325714 1.285714 1.240000 1.388571
> 
> would it be possible to you please, to send me some comments on what
> that
> command does, and where I might learn the math behind it?
> 
> 
> Thank you very much in advance.
> 
> All the best,
> 
> Tiago
> 
> 
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> 
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