Problem installing packages

I am installing Matrix on a Linux x86_64 multicore system. I receive a message:

Warning message:
In install.开发者_开发知识库packages("Matrix", dependencies = TRUE) :
  package 'Matrix' is not available

Sure enough, there are not many details on package troubleshooting. It appears that Matrix is available for x86_64, but it's not available in any repository. How come?

What happens when you do this (and ti doesn't require su or sudo):

R> repos <- "http://cran.r-project.org"
R> AP <- available.packages(contrib.url(repos))
R> AP[ which(AP[,1]=="Matrix"), 1:3]
      Package       Version      Priority 
     "Matrix" "0.999375-38" "recommended" 
R> 

The only time I ran into issue similar to the one you are reporting was when my R version was out of sync with how the repo is organized (ie too old).