Dear R-users,
a question concerning sparse matrices in package "spam" (spam_0.29-2).
On one hand I have a spam object (n X n) from which I cannot compute the
inverse. On the other hand, if I convert this object in a plain matrix, I can
find the inverse without any problem.
Specifically I get the following error message:
Error in chol.spam(a, ...) :
Singularity problem when calculating the Cholesky factor.
Obviously I get similar behaviour when I compute determinants of these objects.
Please see below a toy-example which I created based on my actual problem.
Thanks in advance for any help,
GC
library(spam)
## creating a spam matrix A
ent <- c(2312.12324929972,-2000,1000,-2000,1000,-2000,
5031.91011235955,-2000,-2000,1000,-1,1000,-2000,
2049.8595505618,-2000,1000,-1,-2000,5036.89635854342,
-2000,1000,-2000,1,-2000,-2000,8119.66292134831,-2000,
-2000,-2000,1000,-2000,5058.83426966292,-2000,-1,1000,
-2000,2051.85434173669,-2000,1000,1,1000,-2000,-2000,
5043.87640449438,-2000,1,1000,-2000,1000,-2000,
2110.68820224719,-1,1,0,-1,1,-1,1)
rr <- as.integer(c(1,6,12,18,24,29,35,41,47,52,55,57,59))
cc <- as.integer(c(1,2,3,4,7,1,2,3,5,8,10,1,2,3,6,9,11,1,
4,5,6,7,10,2,4,5,6,8,3,4,5,6,9,12,1,4,
7,8,9,11,2,5,7,8,9,12,3,6,7,8,9,2,4,10,3,7,6,8))
di <- as.integer(c(12,12))
A <- new("spam",
entries=ent,
colindices=cc,
rowpointers=rr,
dimension=di)
## calculate the determinant
det(A)
## computes the inverse
solve(A)
## transform A in a plain matrix
A1 <- matrix(c(A), di)
## calculate the determinant
det(A1)
## computes the inverse
solve(A1)
> version
_
platform i686-pc-linux-gnu
arch i686
os linux-gnu
system i686, linux-gnu
status
major 2
minor 14.1
year 2011
month 12
day 22
svn rev 57956
language R
version.string R version 2.14.1 (2011-12-22)
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