[R] Matrix Multiplication

Gavin Simpson gavin.simpson at ucl.ac.uk
Fri Feb 6 16:57:00 CET 2009


On Fri, 2009-02-06 at 04:57 -0800, Maithili Shiva wrote:
> Hi R helpers,
> 
> 
> 
> I have two matrices A and B of the order (4 * 5) and (5 * 3)
> respectively. How to multiply these two matrices to obtain resultant
> matrix of the order (4 * 3). 

?`%*%`

E.g.:

> A <- matrix(runif(4*5), nrow = 4)
> B <- matrix(rnorm(5*3), nrow = 5)
> A %*% B
            [,1]      [,2]      [,3]
[1,]  0.11087765 0.1172641 -1.965684
[2,]  0.08811864 0.6628032 -2.704704
[3,] -0.99875302 1.2822072 -1.388777
[4,] -1.01109686 1.5752980 -1.560827

> 
> Thanks in advance
> 
> With regards
> 
> Maithili

HTH

G
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