lotri
Easily Specify block-diagonal matrices with (lo)wer (tri)angular matrices. Its as if you have won the (badly spelled) lotri (or lottery).
This was made to allow people (like me) to specify lower triangular
matrices similar to the domain specific language implemented in
nlmixr. Originally I had it included in RxODE
, but thought it may
have more general applicability, so I separated it into a new
package.
For me, specifying the matricies in this way is easier than specifying them using R's default matrix. For instance to fully specify a simple 2x2 matrix, in R you specify:
mat <- matrix(c(1, 0.5, 0.5, 1),nrow=2,ncol=2,dimnames=list(c("a", "b"), c("a", "b")))
With lotri
, you simply specify:
library(lotri)
mat <- lotri(a+b ~ c(1,
0.5, 1))
I find it more legible and easier to specify, especially if you have a more complex matrix. For instance with the more complex matrix:
mat <- lotri({
a+b ~ c(1,
0.5, 1)
c ~ 1
d +e ~ c(1,
0.5, 1)
})
To fully specify this in base R you would need to use:
mat <- matrix(c(1, 0.5, 0, 0, 0,
0.5, 1, 0, 0, 0,
0, 0, 1, 0, 0,
0, 0, 0, 1, 0.5,
0, 0, 0, 0.5, 1),
nrow=5, ncol=5,
dimnames= list(c("a", "b", "c", "d", "e"), c("a", "b", "c", "d", "e")))
Of course with the excellent Matrix
package this is a bit easier:
library(Matrix)
mat <- matrix(c(1, 0.5, 0.5, 1),nrow=2,ncol=2,dimnames=list(c("a", "b"), c("a", "b")))
mat <- bdiag(list(mat, matrix(1), mat))
## Convert back to standard matrix
mat <- as.matrix(mat)
##
dimnames(mat) <- list(c("a", "b", "c", "d", "e"), c("a", "b", "c", "d", "e"))
Regardless, I think lotri
is a bit easier to use.