[R] Huge matrix: allocation works but assignment fails

[Remi]

Hello everyone,

I am working with one big matrix:
w=matrix(0,18000,18000)

on a Linux computer with 16Go of RAM.

I can actually create the matrix, and even access elements:
w[10,10]
0

but if I try to change one element, it fails:
w[10,10]=1
Erreur : impossible d'allouer un vecteur de taille 2531250 Ko
(Failed to allocate a vector of size...)

What can I do? And, maybe even more important, how can one explains such 
a behavior?

Thank you for any help/advice

Rémi Proville.