116 lines
3.6 KiB
C
116 lines
3.6 KiB
C
// 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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