add: ttm C implementation
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#' Tensor Times Matrix (n-mode tensor matrix product)
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#'
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#' @param T array of order at least \code{mode}
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#' @param M matrix, the right hand side of the mode product such that
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#' \code{ncol(M)} equals \code{dim(T)[mode]}
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#' @param mode the mode of the product in the range \code{1:length(dim(T))}
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#'
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#' @returns multi-dimensional array of the same order as \code{T} with the
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#' \code{mode} dimension equal to \code{nrow(M)}
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#'
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#' @export
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ttm <- function(T, M, mode = length(dim(T))) {
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mode <- as.integer(mode)
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dims <- dim(T)
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if (length(dims) < mode) {
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stop(sprintf("Mode (%d) must be smaller equal the tensor order %d",
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mode, length(dims)))
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}
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if (dims[mode] != ncol(M)) {
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stop(sprintf("Dim. missmatch, mode %d has dim %d but ncol is %d.",
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mode, dims[mode], ncol(M)))
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}
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# Special case of mode being equal to tensor order, then an alternative
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# (but more efficient) version is Z M' where Z is only the reshaped but
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# no permutation of elements is required (as in the case of mode 1)
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if (mode == length(dims)) {
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# Convert tensor to matrix (similar to matricization)
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dim(T) <- c(prod(dims[-mode]), dims[mode])
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# Equiv matrix product
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C <- tcrossprod(T, M)
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# Shape back to tensor
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dim(C) <- c(dims[-mode], nrow(M))
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C
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} else {
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# Matricize tensor T
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if (mode != 1L) {
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perm <- c(mode, seq_along(dims)[-mode])
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T <- aperm(T, perm)
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}
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dim(T) <- c(dims[mode], prod(dims[-mode]))
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# Perform equivalent matrix multiplication
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C <- M %*% T
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# Reshape and rearrange matricized result back to a tensor
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dim(C) <- c(nrow(M), dims[-mode])
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if (mode == 1L) {
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C
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} else {
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aperm(C, order(perm))
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}
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}
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}
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#' @rdname ttm
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#' @export
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`%x_1%` <- function(T, M) ttm(T, M, 1L)
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#' @rdname ttm
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#' @export
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`%x_2%` <- function(T, M) ttm(T, M, 2L)
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#' @rdname ttm
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#' @export
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`%x_3%` <- function(T, M) ttm(T, M, 3L)
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#' @rdname ttm
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#' @export
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`%x_4%` <- function(T, M) ttm(T, M, 4L)
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@ -0,0 +1,28 @@
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#' Tensor Times Matrix (n-mode tensor matrix product)
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#'
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#' @param T array of order at least \code{mode}
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#' @param M matrix, the right hand side of the mode product such that
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#' \code{ncol(M)} equals \code{dim(T)[mode]}
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#' @param mode the mode of the product in the range \code{1:length(dim(T))}
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#'
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#' @returns multi-dimensional array of the same order as \code{T} with
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#' \code{mode} dimension equal to \code{nrow(M)}
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#'
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#' @export
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ttm <- function(T, M, mode = length(dim(T))) {
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storage.mode(T) <- storage.mode(M) <- "double"
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.Call("C_ttm", T, M, as.integer(mode))
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}
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#' @rdname ttm
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#' @export
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`%x_1%` <- function(T, M) ttm(T, M, 1L)
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#' @rdname ttm
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#' @export
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`%x_2%` <- function(T, M) ttm(T, M, 2L)
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#' @rdname ttm
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#' @export
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`%x_3%` <- function(T, M) ttm(T, M, 3L)
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#' @rdname ttm
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#' @export
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`%x_4%` <- function(T, M) ttm(T, M, 4L)
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@ -0,0 +1,23 @@
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#include <R.h>
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#include <Rinternals.h>
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#include <R_ext/Rdynload.h>
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// extern SEXP FastPOI_C_sub(SEXP in_B, SEXP in_Delta,
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// SEXP in_lambda, SEXP in_maxit, SEXP in_tol
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// );
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/* Tensor Times Matrix a.k.a. Mode Product */
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extern SEXP ttm(SEXP A, SEXP X, SEXP mode);
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/* List of registered routines (e.g. C entry points) */
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static const R_CallMethodDef CallEntries[] = {
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// {"FastPOI_C_sub", (DL_FUNC) &FastPOI_C_sub, 5}, // NOT USED
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{"C_ttm", (DL_FUNC) &ttm, 3},
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{NULL, NULL, 0}
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};
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/* Restrict C entry points to registered routines. */
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void R_init_tensorPredictors(DllInfo *dll) {
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R_registerRoutines(dll, NULL, CallEntries, NULL, NULL);
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R_useDynamicSymbols(dll, FALSE);
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}
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// The need for `USE_FC_LEN_T` and `FCONE` is due to a Fortran character string
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// to C incompatibility. See: Writing R Extentions: 6.6.1 Fortran character strings
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#define USE_FC_LEN_T
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#include <R.h>
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#include <Rinternals.h>
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#include <R_ext/BLAS.h>
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#ifndef FCONE
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#define FCONE
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#endif
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/**
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* Tensor Times Matrix a.k.a. Mode Product
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*
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* @param A multi-dimensionl array
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* @param B matrix
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* @param m mode index (1-indexed)
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*/
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extern SEXP ttm(SEXP A, SEXP B, SEXP m) {
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// get zero indexed mode
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int mode = asInteger(m) - 1;
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// get dimension attribute of A
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SEXP dim = getAttrib(A, R_DimSymbol);
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// validate mode (mode must be smaller than the nr of dimensions)
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if (mode < 0 || length(dim) <= mode) {
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error("Illegal mode");
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}
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// and check if B is a matrix of non degenetate size
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if (!isMatrix(B)) {
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error("Expected a matrix as second argument");
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}
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if (!nrows(B) || !ncols(B)) {
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error("Zero dimension detected");
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}
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// check matching of dimensions
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if (INTEGER(dim)[mode] != ncols(B)) {
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error("Dimension missmatch (mode dim not equal to ncol)");
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}
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// calc nr of response elements `prod(dim(X)[-mode]) * ncol(X)`,
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int leny = 1;
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// and the strides
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// `stride[0] <- prod(dim(X)[seq_len(mode - 1)])`
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// `stride[1] <- dim(X)[mode]`
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// `stride[2] <- prod(dim(X)[-seq_len(mode)])`
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int stride[3] = {1, INTEGER(dim)[mode], 1};
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for (int i = 0; i < length(dim); ++i) {
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int size = INTEGER(dim)[i];
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// check for non-degenetate dimensions
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if (!size) {
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error("Zero dimension detected");
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}
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leny *= (i == mode) ? nrows(B) : size;
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stride[0] *= (i < mode) ? size : 1;
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stride[2] *= (i > mode) ? size : 1;
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}
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// as well as the matrix rows (cols only needed once)
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int nrow = nrows(B);
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// create response object C
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SEXP C = PROTECT(allocVector(REALSXP, leny));
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// raw data access pointers
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double* a = REAL(A);
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double* b = REAL(B);
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double* c = REAL(C);
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// Tensor Times Matrix / Mode Product
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const double zero = 0.0;
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const double one = 1.0;
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if (mode == 0) {
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// mode 1: (A x_1 B)_(1) = B A_(1) as a single Matrix-Matrix prod
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F77_CALL(dgemm)("N", "N", &nrow, &stride[2], &stride[1], &one,
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b, &nrow, a, &stride[1],
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&zero, c, &nrow FCONE FCONE);
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} else {
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// Other modes can be written as blocks of matrix multiplications
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for (int i2 = 0; i2 < stride[2]; ++i2) {
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F77_CALL(dgemm)("N", "T", &stride[0], &nrow, &stride[1], &one,
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&a[i2 * stride[0] * stride[1]], &stride[0], b, &nrow,
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&zero, &c[i2 * stride[0] * nrow], &stride[0] FCONE FCONE);
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}
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}
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/*
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// Tensor Times Matrix / Mode Product (reference implementation)
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memset(c, 0, leny * sizeof(double));
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for (int i2 = 0; i2 < stride[2]; ++i2) {
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for (int i1 = 0; i1 < stride[1]; ++i1) { // stride[1] == ncols(B)
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for (int j = 0; j < nrow; ++j) {
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for (int i0 = 0; i0 < stride[0]; ++i0) {
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c[i0 + (j + i2 * nrow) * stride[0]] +=
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a[i0 + (i1 + i2 * stride[1]) * stride[0]] * b[j + i1 * nrow];
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}
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}
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}
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}
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*/
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// finally, set result dimensions
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SEXP newdim = PROTECT(allocVector(INTSXP, length(dim)));
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for (int i = 0; i < length(dim); ++i) {
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INTEGER(newdim)[i] = (i == mode) ? nrows(B) : INTEGER(dim)[i];
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}
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setAttrib(C, R_DimSymbol, newdim);
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// release C to the hands of the garbage collector
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UNPROTECT(2);
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return C;
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}
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