Hi,
I am trying to find an elegant way to compute and store some
frequently used matrices "on demand". The Matrix package already uses
something like this for storing decompositions, but I don't know how
to do it.
The actual context is the following:
A list has information about a basis of a B-spline space (nodes,
order) and gridpoints at which the basis functions would be evaluated
(not necessarily the nodes). Something like this:
bsplinegrid <- list(nodes=1:8,order=4,grid=seq(2,5,by=.2))
I need the design matrix (computed by splineDesign) for various
derivatives (not necessarily known in advance), to be calculated by
the function
bsplinematrix <- function(bsplinegrid, deriv=0) {
x <- bsplinegrid$grid
Matrix(splineDesign(bslinegrid$knots, x, ord=basis$order,
derivs = rep(deriv,length(x))))
}
However, I don't want to call splineDesign all the time. A smart way
would be storing the calculated matrices in a list inside bsplinegrid.
Pseudocode would look like this:
bsplinematrix <- function(bsplinegrid, deriv=0) {
if (is.null(bsplinegrid$matrices[[deriv+1]])) {
## compute the matrix and put it in the list bsplinegrid$matrices,
## but not of the local copy
}
bsplinegrid$matrices[[deriv+1]]
}
My problem is that I don't know how to modify bsplinegrid$matrices
outside the function -- assignment inside would only modify the local
copy.
Any help would be appreciated -- I wanted to learn how Matrix does it,
but don't know how to display the source with s3 methods (getAnywhere
doesn't work).
Tamas
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