Multiplication by Factors from Matrix Factorizations

Multiplies a matrix or vector on the left or right by a factor from a matrix factorization or its transpose.

facmul(x, factor, y, trans = FALSE, left = TRUE, ...)

Arguments

x: a MatrixFactorization object.
factor: a character string indicating a factor in the factorization represented by x, typically an element of names(expand2(x, ...)).
y: a matrix or vector to be multiplied on the left or right by the factor or its transpose.
trans: a logical indicating if the transpose of the factor should be used, rather than the factor itself.
left: a logical indicating if the y should be multiplied on the left by the factor, rather than on the right.
...: further arguments passed to or from methods.

Value

The value of op(M) %*% y or y %*% op(M), depending on left, where M is the factor (always without dimnames) and op(M) is M or t(M), depending on trans.

Details

facmul is experimental and currently no methods are exported from Matrix.

Examples

## Conceptually, methods for 'facmul' _would_ behave as follows ...
if (FALSE) { # \dontrun{
n <- 3L
x <- lu(Matrix(rnorm(n * n), n, n))
y <- rnorm(n)
L <- unname(expand2(x)[[nm <- "L"]])
stopifnot(exprs = {
    all.equal(facmul(x, nm, y, trans = FALSE, left =  TRUE), L %*% y)
    all.equal(facmul(x, nm, y, trans = FALSE, left = FALSE), y %*% L)
    all.equal(facmul(x, nm, y, trans =  TRUE, left =  TRUE),  crossprod(L, y))
    all.equal(facmul(x, nm, y, trans =  TRUE, left = FALSE), tcrossprod(y, L))
})
} # }