Hi,
I have sparse (tridiagonal) matrices, and I use the Matrix package for
handling them. For certain computations, I need to either set the
first row to zero, or double the last row. I find that neither
operation preserves sparsity, eg
> m <- Diagonal(5)
> m
5 x 5 diagonal matrix of class "ddiMatrix"
[,1] [,2] [,3] [,4] [,5]
[1,] 1 . . . .
[2,] . 1 . . .
[3,] . . 1 . .
[4,] . . . 1 .
[5,] . . . . 1
> m[1,] <- 0
> m
5 x 5 Matrix of class "dgeMatrix"
[,1] [,2] [,3] [,4] [,5]
[1,] 0 0 0 0 0
[2,] 0 1 0 0 0
[3,] 0 0 1 0 0
[4,] 0 0 0 1 0
[5,] 0 0 0 0 1
> m <- Diagonal(5)
> rbind(m,1:5)
6 x 5 Matrix of class "dgeMatrix"
[,1] [,2] [,3] [,4] [,5]
[1,] 1 0 0 0 0
[2,] 0 1 0 0 0
[3,] 0 0 1 0 0
[4,] 0 0 0 1 0
[5,] 0 0 0 0 1
[6,] 1 2 3 4 5
Currently, I am calling Matrix to make these sparse again, but my
matrices are large (100x100). Is there a way to perform the
operations I want without losing sparsity?
Thanks,
Tamas
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