32 lines
640 B
R
32 lines
640 B
R
#' Multi Kronecker Multiplication
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#'
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#' \deqn{C = A (B_1\otimes ...\otimes B_r)}{%
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#' C = A (B_1 %x% ... %x% B_r)}
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#'
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#' @examples
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#' n <- 17
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#' p <- c(2, 7, 11)
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#' q <- c(3, 5, 13)
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#'
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#' A <- matrix(rnorm(n * prod(p)), n)
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#' Bs <- Map(matrix, Map(rnorm, p * q), p)
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#'
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#' stopifnot(all.equal(
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#' A %*% Reduce(`%x%`, Bs),
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#' mkm(A, Bs)
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#' ))
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#'
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#' @export
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mkm <- function(A, Bs) {
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# reshape
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dim(A) <- c(nrow(A), rev(mapply(nrow, Bs)))
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# perform equiv Multi Linear Multiplication
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C <- mlm(A, rev(Bs), seq_along(Bs) + 1, transposed = TRUE)
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# reshape back
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dim(C) <- c(nrow(C), prod(dim(C)[-1]))
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C
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}
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