Making use of the row() and col() functions speeds things up a bit.
makeMatrix2 <- function(a, b, dim) {
X <- matrix(NA, ncol=dim, nrow=dim)
X <- exp( (-1*abs(row(X) - col(X)))/(3*b) )
diag(X) <- a
X
}
system.time(makeMatrix(1, 2, 1000))
system.time(makeMatrix2(1, 2, 1000))
Jean
`·.,, ><(((º> `·.,, ><(((º> `·.,, ><(((º>
Jean V. Adams
Statistician
U.S. Geological Survey
Great Lakes Science Center
223 East Steinfest Road
Antigo, WI 54409 USA
From:
monk <m...@hush.com>
To:
r-help@r-project.org
Date:
08/01/2011 01:20 PM
Subject:
[R] fill Matrix quicker
Sent by:
r-help-boun...@r-project.org
dear all,
i have a quite simple question, i want to fill up a Matrix like done in
the
following function,
but the performance is very bad for large dimensions
is there a way to do this like with apply or something similar?
makeMatrix <- function(a, b,dim) {
X=matrix(0,ncol=dim,nrow=dim)
for (i in c(1:dim)){
for (j in c(1:dim)) {
if (i==j) {X[i,j]<-a}
else { X[i,j]<- exp((
-1*abs(i-j))/(3*b)) }
}
}
X
}
--
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and provide commented, minimal, self-contained, reproducible code.
