On Thu, 13 Aug 2009 15:11:03 +0200, Michael Knudsen <micknud...@gmail.com>
wrote:
On Thu, Aug 13, 2009 at 11:35 AM, Lina Rusyte<liner...@yahoo.co.uk>
wrote:
Hi Lina,
What function can I use for matrices addition? I couldn’t find any
information about it in the manual or in the internet.
(A+B suits, when the number of matrixes is small, function sum()
doesn’t suit for matrices addition, because it sums all variables in
the matrices and produces as an answer single number, not a matrix).
Reduce is the function you need. It can be applied to any operator not
just `+`:
M_list <- replicate(4, matrix(1, 2, 2), simplify=FALSE)
M_list
[[1]]
[,1] [,2]
[1,] 1 1
[2,] 1 1
[[2]]
[,1] [,2]
[1,] 1 1
[2,] 1 1
[[3]]
[,1] [,2]
[1,] 1 1
[2,] 1 1
[[4]]
[,1] [,2]
[1,] 1 1
[2,] 1 1
Reduce(`+`, M_list)
[,1] [,2]
[1,] 4 4
[2,] 4 4
I don't know of any function doing that, but you could easily write a
one yourself. Suppese that X is a list of matrices. Then you could
e.g. do as follows:
matrixSum = function(X)
{
N = length(X)
if (N==2) return(X[[1]]+X[[2]])
else return(matrixSum(X[[1:(N-1)]],X[[N]]))
}
I guess that one should do the trick.
Best,
Michael
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