What does the command diag(solve(matrix)) do?

2 messages · tiago.pereira at mbe.bio.br, Peter Alspach

Original

tiago.pereira at mbe.bio.br

Tue, Apr 12, 2011 5:43 PM #

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:

[,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))

[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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Tue, Apr 12, 2011 10:06 PM #

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

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