# [R] Matrix: Help with syntax and comparison with SparseM

Nicholas Lewin-Koh nikko at hailmail.net
Fri Jun 25 09:30:44 CEST 2004

```Hi,
I am writing some basic smoothers in R for cleaning some spectral data.
I wanted to see if I could get close to matlab for speed, so I was
trying to compare SparseM
with Matrix to see which could do the choleski decomposition the
fastest.

Here is the function using SparseM
difsm <- function(y, lambda, d){
# Smoothing with a finite difference penalty
# y:      signal to be smoothed
# lambda: smoothing parameter
# d:      order of differences in penalty (generally 2)
# based on code by Paul Eilers 2002
require(SparseM)
m <- length(y)
E <- as(m,"matrix.diag.csr")
D <- diff(E,differences=d)
B <- E + (lambda * t(D)%*%D)
z <- solve(B,y)
z
}

To do this in Matrix, I am not sure how to get an Identity matrix of
dimension m. From looking at the documentation I would think that
E<-new("cscMatrix", nrow=m, i=integer(m),x=rep(1,m),p=0:(m-1)))
Should do what I want, but it fails?
> m<-10
> E<-new("cscMatrix", nrow=m, i=integer(m),x=rep(1,m),p=0:(m-1))
Error in initialize(value, ...) : Invalid names for slots of class
cscMatrix: nrow
> E<-new("cscMatrix", i=integer(m),x=rep(1,m),p=0:(m-1))
Error in validObject(.Object) : Invalid "cscMatrix" object: last element
of slot p must match length of slots i and x

Granted I am not very fascile with the S4 classes, so I may be doing
something stupid.
Also to do the next step there is no diff method for matrices in Matrix,
that would be nice
:)

I guess the last step would be easy
z <- solve((E + (lambda * crossprod(D))),y)

But I can't get the Identity matrix???

Thanks for the help,
it is probably obvious, but I am missing it.

Nicholas

```