[R] matrix inverstion

[Rosario Garcia Gil]

Hello

I have this matrix which I am trying to invert. I get a message about reciprocal condition number, what that does mean?

> XT_X
     [,1] [,2] [,3] [,4] [,5]
[1,]    3    0    0    2    1
[2,]    0    2    0    1    1
[3,]    0    0    2    1    1
[4,]    2    1    1    4    0
[5,]    1    1    1    0    3
> iXT_X <- solve(XT_X)
Error in solve.default(XT_X) : 
  system is computationally singular: reciprocal condition number = 1.11022e-17


Thanks
Rosario