Avoiding loop

Hi:

Try the expm package. Using your example,

R = A%*%B
for(i in 1:100)

+ {
+        R = R%*%B
+ }

R

[,1]         [,2]         [,3]         [,4]         [,5]
[1,] 9.934879e+47 1.098761e+48 8.868476e+47 7.071831e+47 6.071370e+47
[2,] 1.492692e+48 1.650862e+48 1.332468e+48 1.062526e+48 9.122090e+47
[3,] 6.693145e+47 7.402373e+47 5.974708e+47 4.764305e+47 4.090293e+47
[4,] 5.895689e+47 6.520416e+47 5.262850e+47 4.196661e+47 3.602954e+47
[5,] 8.347321e+47 9.231830e+47 7.451326e+47 5.941778e+47 5.101187e+47

library(expm)
# The matrix power function is an operator % ^ %

A %*% (B %^% 101)

[,1]         [,2]         [,3]         [,4]         [,5]
[1,] 9.934879e+47 1.098761e+48 8.868476e+47 7.071831e+47 6.071370e+47
[2,] 1.492692e+48 1.650862e+48 1.332468e+48 1.062526e+48 9.122090e+47
[3,] 6.693145e+47 7.402373e+47 5.974708e+47 4.764305e+47 4.090293e+47
[4,] 5.895689e+47 6.520416e+47 5.262850e+47 4.196661e+47 3.602954e+47
[5,] 8.347321e+47 9.231830e+47 7.451326e+47 5.941778e+47 5.101187e+47

system.time(replicate(1000, A %*% (B %^% 101)))

user  system elapsed
   0.02    0.00    0.01

system.time(replicate(1000, {R = A%*%B

+     for(i in 1:100)
+ {
+        R = R%*%B
+ }  }))
   user  system elapsed
   0.15    0.00    0.15

HTH,
Dennis

Hi everyone.

I'm using matrix product such as :


#Generate some data
NCols = 5
NRows = 5
A = matrix(runif(NCols*NRows), ncol=NCols)
B = matrix(runif(NCols*NRows), ncol=NCols)

#First calculation
R = A%*%B


for(i in 1:100)
{
? ? ? ?R = R%*%B
}


I would like to know if it was possible to avoid the loop by using something
like mapply or anything else.

Tx in advance,
Phil

--
View this message in context: http://r.789695.n4.nabble.com/Avoiding-loop-tp3457963p3457963.html
Sent from the R help mailing list archive at Nabble.com.

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.