#ifdef __GLIBC__
// to get strdup declared in glibc (when strict -std=c11 or -stdc99):
#define _POSIX_C_SOURCE 200809L
#endif

#include <string.h>

#include "dgCMatrix.h"

/* for Csparse_transpose() : */
#include "Csparse.h"
#include "chm_common.h"
/* -> Mutils.h / SPQR ... */

/* FIXME -- we "forget" about dimnames almost everywhere : */

/* for dgCMatrix  _and_ lgCMatrix and others  (but *not*  ngC...) : */
SEXP xCMatrix_validate(SEXP x)
{
    /* Almost everything now in Csparse_validate ( ./Csparse.c )
     * *but* the checking of the 'x' slot : */
    if (xlength(GET_SLOT(x, Matrix_iSym)) !=
	xlength(GET_SLOT(x, Matrix_xSym)))
	return mkString(_("lengths of slots 'i' and 'x' must match"));

    return ScalarLogical(1);
}

/* for dgRMatrix  _and_ lgRMatrix and others  (but *not*  ngC...) : */
SEXP xRMatrix_validate(SEXP x)
{
    /* Almost everything now in Rsparse_validate ( ./Csparse.c )
     * *but* the checking of the 'x' slot : */
    if (xlength(GET_SLOT(x, Matrix_jSym)) !=
	xlength(GET_SLOT(x, Matrix_xSym)))
	return mkString(_("lengths of slots 'j' and 'x' must match"));

    return ScalarLogical(1);
}

/* This and the following R_to_CMatrix() lead to memory-not-mapped seg.faults
 * only with {32bit + R-devel + enable-R-shlib} -- no idea why */
SEXP compressed_to_TMatrix(SEXP x, SEXP colP)
{
    int col = asLogical(colP); /* 1 if "C"olumn compressed;  0 if "R"ow */
    /* however, for Csparse, we now effectively use the cholmod-based
     * Csparse_to_Tsparse() in ./Csparse.c ; maybe should simply write
     * an  as_cholmod_Rsparse() function and then do "as there" ...*/
    SEXP indSym = col ? Matrix_iSym : Matrix_jSym, ans,
	indP = PROTECT(GET_SLOT(x, indSym)),
	  pP = PROTECT(GET_SLOT(x, Matrix_pSym));
    int npt = length(pP) - 1;
    char *ncl = strdup(class_P(x));
    static const char *valid[] = { MATRIX_VALID_Csparse, MATRIX_VALID_Rsparse, ""};
    int ctype = R_check_class_etc(x, valid);

    if (ctype < 0)
	error(_("invalid class(x) '%s' in compressed_to_TMatrix(x)"), ncl);

    /* replace 'C' or 'R' with 'T' :*/
    ncl[2] = 'T';
    ans = PROTECT(NEW_OBJECT_OF_CLASS(ncl));

    slot_dup(ans, x, Matrix_DimSym);
    if((ctype / 3) % 4 != 2) /* not n..Matrix */
	slot_dup(ans, x, Matrix_xSym);
    if(ctype % 3) { /* s(ymmetric) or t(riangular) : */
	slot_dup(ans, x, Matrix_uploSym);
	if(ctype % 3 == 2) /* t(riangular) : */
	    slot_dup(ans, x, Matrix_diagSym);
    }
    SET_DimNames(ans, x);
    // possibly asymmetric for symmetricMatrix is ok
    SET_SLOT(ans, indSym, duplicate(indP));
    expand_cmprPt(npt, INTEGER(pP),
		  INTEGER(ALLOC_SLOT(ans, col ? Matrix_jSym : Matrix_iSym,
				     INTSXP, length(indP))));
    free(ncl);
    UNPROTECT(3);
    return ans;
}

SEXP R_to_CMatrix(SEXP x)
{
    SEXP ans, tri = PROTECT(allocVector(LGLSXP, 1));
    char *ncl = strdup(class_P(x));
    static const char *valid[] = { MATRIX_VALID_Rsparse, ""};
    int ctype = R_check_class_etc(x, valid);
    int *x_dims = INTEGER(GET_SLOT(x, Matrix_DimSym)), *a_dims;
    PROTECT_INDEX ipx;

    if (ctype < 0)
	error(_("invalid class(x) '%s' in R_to_CMatrix(x)"), ncl);

    /* replace 'R' with 'C' : */
    ncl[2] = 'C';
    PROTECT_WITH_INDEX(ans = NEW_OBJECT_OF_CLASS(ncl), &ipx);

    a_dims = INTEGER(ALLOC_SLOT(ans, Matrix_DimSym, INTSXP, 2));
    /* reversed dim() since we will transpose: */
    a_dims[0] = x_dims[1];
    a_dims[1] = x_dims[0];

    /* triangular: */ LOGICAL(tri)[0] = 0;
    if((ctype / 3) != 2) /* not n..Matrix */
	slot_dup(ans, x, Matrix_xSym);
    if(ctype % 3) { /* s(ymmetric) or t(riangular) : */
	SET_SLOT(ans, Matrix_uploSym,
		 mkString((*uplo_P(x) == 'U') ? "L" : "U"));
	if(ctype % 3 == 2) { /* t(riangular) : */
	    LOGICAL(tri)[0] = 1;
	    slot_dup(ans, x, Matrix_diagSym);
	}
    }
    SET_SLOT(ans, Matrix_iSym, duplicate(GET_SLOT(x, Matrix_jSym)));
    slot_dup(ans, x, Matrix_pSym);
    REPROTECT(ans = Csparse_transpose(ans, tri), ipx);
    SET_DimNames(ans, x);
    // possibly asymmetric for symmetricMatrix is ok
    free(ncl);
    UNPROTECT(2);
    return ans;
}

/** Return a 2 column matrix  '' cbind(i, j) ''  of 0-origin index vectors (i,j)
 *  which entirely correspond to the (i,j) slots of
 *  as(x, "TsparseMatrix") :
 */
SEXP compressed_non_0_ij(SEXP x, SEXP colP)
{
    int col = asLogical(colP); /* 1 if "C"olumn compressed;  0 if "R"ow */
    SEXP ans, indSym = col ? Matrix_iSym : Matrix_jSym;
    SEXP indP = PROTECT(GET_SLOT(x, indSym)),
	 pP   = PROTECT(GET_SLOT(x, Matrix_pSym));
    int i, *ij;
    int nouter = INTEGER(GET_SLOT(x, Matrix_DimSym))[col ? 1 : 0],
	n_el   = INTEGER(pP)[nouter]; /* is only == length(indP), if the
				     inner slot is not over-allocated */

    ij = INTEGER(ans = PROTECT(allocMatrix(INTSXP, n_el, 2)));
    /* expand the compressed margin to 'i' or 'j' : */
    expand_cmprPt(nouter, INTEGER(pP), &ij[col ? n_el : 0]);
    /* and copy the other one: */
    if (col)
	for(i = 0; i < n_el; i++)
	    ij[i] = INTEGER(indP)[i];
    else /* row compressed */
	for(i = 0; i < n_el; i++)
	    ij[i + n_el] = INTEGER(indP)[i];

    UNPROTECT(3);
    return ans;
}

#if 0				/* unused */
SEXP dgCMatrix_lusol(SEXP x, SEXP y)
{
    SEXP ycp = PROTECT((TYPEOF(y) == REALSXP) ?
		       duplicate(y) : coerceVector(y, REALSXP));
    CSP xc = AS_CSP__(x);
    R_CheckStack();

    if (xc->m != xc->n || xc->m <= 0)
	error(_("dgCMatrix_lusol requires a square, non-empty matrix"));
    if (LENGTH(ycp) != xc->m)
	error(_("Dimensions of system to be solved are inconsistent"));
    if (!cs_lusol(/*order*/ 1, xc, REAL(ycp), /*tol*/ 1e-7))
	error(_("cs_lusol failed"));

    UNPROTECT(1);
    return ycp;
}
#endif

// called from package MatrixModels's R code
SEXP dgCMatrix_qrsol(SEXP x, SEXP y, SEXP ord)
{
    /* FIXME: extend this to work in multivariate case, i.e. y a matrix with > 1 column ! */
    SEXP ycp = PROTECT((TYPEOF(y) == REALSXP) ?
		       duplicate(y) : coerceVector(y, REALSXP));
    CSP xc = AS_CSP(x); /* <--> x  may be  dgC* or dtC* */
    int order = asInteger(ord);
#ifdef _not_yet_do_FIXME__
    const char *nms[] = {"L", "coef", "Xty", "resid", ""};
    SEXP ans = PROTECT(Rf_mkNamed(VECSXP, nms));
#endif
    R_CheckStack();

    if (order < 0 || order > 3)
	error(_("dgCMatrix_qrsol(., order) needs order in {0,..,3}"));
    /* --> cs_amd()  ---  order 0: natural, 1: Chol, 2: LU, 3: QR */
    if (LENGTH(ycp) != xc->m)
	error(_("Dimensions of system to be solved are inconsistent"));
    /* FIXME?  Note that qr_sol() would allow *under-determined systems;
     *		In general, we'd need  LENGTH(ycp) = max(n,m)
     * FIXME also: multivariate y (see above)
     */
    if (xc->m < xc->n || xc->n <= 0)
	error(_("dgCMatrix_qrsol(<%d x %d>-matrix) requires a 'tall' rectangular matrix"),
		xc->m, xc->n);

    /* cs_qrsol(): Tim Davis (2006) .. "8.2 Using a QR factorization", p.136f , calling
     * -------      cs_sqr(order, ..), see  p.76 */
    /* MM: FIXME: write our *OWN* version of - the first case (m >= n) - of cs_qrsol()
     * ---------  which will  (1) work with a *multivariate* y
     *                        (2) compute coefficients properly, not overwriting RHS
     */
    if (!cs_qrsol(order, xc, REAL(ycp)))
	/* return value really is 0 or 1 - no more info there */
	error(_("cs_qrsol() failed inside dgCMatrix_qrsol()"));

    /* Solution is only in the first part of ycp -- cut its length back to n : */
    ycp = lengthgets(ycp, (R_xlen_t) xc->n);

    UNPROTECT(1);
    return ycp;
}

// Modified version of Tim Davis's cs_qr_mex.c file for MATLAB (in CSparse)
//  Usage: [V,beta,p,R,q] = cs_qr(A) ;
SEXP dgCMatrix_QR(SEXP Ap, SEXP order, SEXP keep_dimnames)
{
    CSP A = AS_CSP__(Ap), D;
    int io = INTEGER(order)[0];
    Rboolean verbose = (io < 0);// verbose=TRUE, encoded with negative 'order'
    int m0 = A->m, m = m0, n = A->n, ord = asLogical(order) ? 3 : 0, *p;
    R_CheckStack();

    if (m < n) error(_("A must have #{rows} >= #{columns}")) ;
    SEXP ans = PROTECT(NEW_OBJECT_OF_CLASS("sparseQR"));
    int *dims = INTEGER(ALLOC_SLOT(ans, Matrix_DimSym, INTSXP, 2));
    dims[0] = m; dims[1] = n;
    css *S = cs_sqr(ord, A, 1);	/* symbolic QR ordering & analysis*/
    if (!S) error(_("cs_sqr failed"));
    int keep_dimnms = asLogical(keep_dimnames);
    if(keep_dimnms == NA_LOGICAL) { keep_dimnms = TRUE;
	warning(_("dgcMatrix_QR(*, keep_dimnames = NA): NA taken as TRUE"));
    }
    if(verbose && S->m2 > m) // in ./cs.h , m2 := # of rows for QR, after adding fictitious rows
	Rprintf("Symbolic QR(): Matrix structurally rank deficient (m2-m = %d)\n",
		S->m2 - m);
    csn *N = cs_qr(A, S);		/* numeric QR factorization */
    if (!N) error(_("cs_qr failed")) ;
    cs_dropzeros(N->L);		/* drop zeros from V and sort */
    D = cs_transpose(N->L, 1); cs_spfree(N->L);
    N->L = cs_transpose(D, 1); cs_spfree(D);
    cs_dropzeros(N->U);		/* drop zeros from R and sort */
    D = cs_transpose(N->U, 1); cs_spfree(N->U) ;
    N->U = cs_transpose(D, 1); cs_spfree(D);
    m = N->L->m;		/* m may be larger now */
    // MM: m := S->m2  also counting the ficticious rows (Tim Davis, p.72, 74f)
    p = cs_pinv(S->pinv, m);	/* p = pinv' */
    SEXP dn = R_NilValue; Rboolean do_dn = FALSE;
    if(keep_dimnms) {
	dn = GET_SLOT(Ap, Matrix_DimNamesSym);
	do_dn = !isNull(VECTOR_ELT(dn, 0)) && m == m0;
	// FIXME? also deal with case m > m0 ?
	if(do_dn) { // keep rownames
	    dn = PROTECT(duplicate(dn));
	    SET_VECTOR_ELT(dn, 1, R_NilValue);
	} else dn = R_NilValue;
    }
    SET_SLOT(ans, Matrix_VSym, Matrix_cs_to_SEXP(N->L, "dgCMatrix", 0, dn)); // "V"
    Memcpy(REAL(ALLOC_SLOT(ans, Matrix_betaSym, REALSXP, n)), N->B, n);
    Memcpy(INTEGER(ALLOC_SLOT(ans, Matrix_pSym,  INTSXP, m)), p, m);
    if(do_dn) {
	UNPROTECT(1); // dn
	dn = R_NilValue; do_dn = FALSE;
    }
    if (ord) {
	Memcpy(INTEGER(ALLOC_SLOT(ans, install("q"), INTSXP, n)), S->q, n);
	if(keep_dimnms) {
	    dn = GET_SLOT(Ap, Matrix_DimNamesSym);
	    do_dn = !isNull(VECTOR_ELT(dn, 1));
	    if(do_dn) {
		dn = PROTECT(duplicate(dn));
		// permute colnames by S->q :  cn <- cn[ S->q ] :
		SEXP cns = PROTECT(duplicate(VECTOR_ELT(dn, 1)));
		for(int j=0; j < n; j++)
		    SET_STRING_ELT(VECTOR_ELT(dn, 1), j, STRING_ELT(cns, S->q[j]));
		UNPROTECT(1);
		SET_VECTOR_ELT(dn, 0, R_NilValue);
	    } else dn = R_NilValue;
	}
    } else
	ALLOC_SLOT(ans, install("q"), INTSXP, 0);
    SEXP R = PROTECT(Matrix_cs_to_SEXP(N->U, "dgCMatrix", 0, dn));
    SET_SLOT(ans, Matrix_RSym, R); UNPROTECT(1); // R
    if(do_dn) UNPROTECT(1); // dn
    cs_nfree(N);
    cs_sfree(S);
    cs_free(p);
    UNPROTECT(1);
    return ans;
}

#ifdef Matrix_with_SPQR
/**
 * Return a SuiteSparse QR factorization of the sparse matrix A
 *
 * @param Ap (pointer to) a [m x n] dgCMatrix
 * @param ordering integer SEXP specifying the ordering strategy to be used
 *	see SPQR/Include/SuiteSparseQR_definitions.h
 * @param econ integer SEXP ("economy"): number of rows of R and columns of Q
 *      to return. The default is m. Using n gives the standard economy form.
 *      A value less than the estimated rank r is set to r, so econ=0 gives the
 *      "rank-sized" factorization, where nrow(R)==nnz(diag(R))==r.
 * @param tol double SEXP: if tol <= -2 use SPQR's default,
 *                         if -2 < tol < 0, then no tol is used; otherwise,
 *      tol > 0, use as tolerance: columns with 2-norm <= tol treated as 0
 *
 *
 * @return SEXP  "SPQR" object with slots (Q, R, p, rank, Dim):
 *	Q: dgCMatrix; R: dgCMatrix  [subject to change to dtCMatrix FIXME ?]
 *	p: integer: 0-based permutation (or length 0 <=> identity);
 *	rank: integer, the "revealed" rank   Dim: integer, original matrix dim.
 */
SEXP dgCMatrix_SPQR(SEXP Ap, SEXP ordering, SEXP econ, SEXP tol)
{
/* SEXP ans = PROTECT(allocVector(VECSXP, 4)); */
    SEXP ans = PROTECT(NEW_OBJECT_OF_CLASS("SPQR"));

    CHM_SP A = AS_CHM_SP(Ap), Q, R;
    SuiteSparse_long *E, rank;/* not always = int   FIXME  (Windows_64 ?) */

    if ((rank = SuiteSparseQR_C_QR(asInteger(ordering),
				   asReal(tol),/* originally had SPQR_DEFAULT_TOL */
				   (SuiteSparse_long)asInteger(econ),/* originally had 0 */
				   A, &Q, &R, &E, &cl)) == -1)
	error(_("SuiteSparseQR_C_QR returned an error code"));

    slot_dup(ans, Ap, Matrix_DimSym);
/*     SET_VECTOR_ELT(ans, 0, */
/* 		   chm_sparse_to_SEXP(Q, 0, 0, 0, "", R_NilValue)); */
    SET_SLOT(ans, install("Q"),
	     chm_sparse_to_SEXP(Q, 0, 0, 0, "", R_NilValue));

    /* Also gives a dgCMatrix (not a dtC* *triangular*) :
     * may make sense if to be used in the "spqr_solve" routines .. ?? */
/*     SET_VECTOR_ELT(ans, 1, */
/* 		   chm_sparse_to_SEXP(R, 0, 0, 0, "", R_NilValue)); */
    SET_SLOT(ans, Matrix_RSym,
	     chm_sparse_to_SEXP(R, 0, 0, 0, "", R_NilValue));
    cholmod_free_sparse(&Al, &cl);
    cholmod_free_sparse(&R, &cl);
    cholmod_free_sparse(&Q, &cl);
    if (E) {
	int *Er;
	SET_VECTOR_ELT(ans, 2, allocVector(INTSXP, A->ncol));
	Er = INTEGER(VECTOR_ELT(ans, 2));
	for (int i = 0; i < A->ncol; i++) Er[i] = (int) E[i];
	Free(E);
    } else SET_VECTOR_ELT(ans, 2, allocVector(INTSXP, 0));
    SET_VECTOR_ELT(ans, 3, ScalarInteger((int)rank));
    UNPROTECT(1);
    return ans;
}
#endif
/* Matrix_with_SPQR */

/* Modified version of Tim Davis's cs_lu_mex.c file for MATLAB */
void install_lu(SEXP Ap, int order, double tol, Rboolean err_sing, Rboolean keep_dimnms)
{
    // (order, tol) == (1, 1) by default, when called from R.
    SEXP ans;
    css *S;
    csn *N;
    int n, *p, *dims;
    CSP A = AS_CSP__(Ap), D;
    R_CheckStack();

    n = A->n;
    if (A->m != n)
	error(_("LU decomposition applies only to square matrices"));
    if (order) {		/* not using natural order */
	order = (tol == 1) ? 2	/* amd(S'*S) w/dense rows or I */
	    : 1;		/* amd (A+A'), or natural */
    }
    S = cs_sqr(order, A, /*qr = */ 0);	/* symbolic ordering */
    N = cs_lu(A, S, tol);	/* numeric factorization */
    if (!N) {
	if(err_sing)
	    error(_("cs_lu(A) failed: near-singular A (or out of memory)"));
	else {
	    /* No warning: The useR should be careful :
	     * Put  NA  into  "LU" factor */
	    set_factors(Ap, ScalarLogical(NA_LOGICAL), "LU");
	    return;
	}
    }
    cs_dropzeros(N->L);		/* drop zeros from L and sort it */
    D = cs_transpose(N->L, 1);
    cs_spfree(N->L);
    N->L = cs_transpose(D, 1);
    cs_spfree(D);
    cs_dropzeros(N->U);		/* drop zeros from U and sort it */
    D = cs_transpose(N->U, 1);
    cs_spfree(N->U);
    N->U = cs_transpose(D, 1);
    cs_spfree(D);
    p = cs_pinv(N->pinv, n);	/* p=pinv' */
    ans = PROTECT(NEW_OBJECT_OF_CLASS("sparseLU"));
    dims = INTEGER(ALLOC_SLOT(ans, Matrix_DimSym, INTSXP, 2));
    dims[0] = n; dims[1] = n;
    SEXP dn; Rboolean do_dn = FALSE;
    if(keep_dimnms) {
	dn = GET_SLOT(Ap, Matrix_DimNamesSym);
	do_dn = !isNull(VECTOR_ELT(dn, 0));
	if(do_dn) {
	    dn = PROTECT(duplicate(dn));
	    // permute rownames by p :  rn <- rn[ p ] :
	    SEXP rn = PROTECT(duplicate(VECTOR_ELT(dn, 0)));
	    for(int i=0; i < n; i++)
		SET_STRING_ELT(VECTOR_ELT(dn, 0), i, STRING_ELT(rn, p[i]));
	    UNPROTECT(1); // rn
	    SET_VECTOR_ELT(dn, 1, R_NilValue); // colnames(.) := NULL
	}
    }
    SET_SLOT(ans, Matrix_LSym,
	     Matrix_cs_to_SEXP(N->L, "dtCMatrix", 0, do_dn ? dn : R_NilValue));

    if(keep_dimnms) {
	if(do_dn) {
	    UNPROTECT(1); // dn
	    dn = GET_SLOT(Ap, Matrix_DimNamesSym);
	}
	do_dn = !isNull(VECTOR_ELT(dn, 1));
	if(do_dn) {
	    dn = PROTECT(duplicate(dn));
	    if(order) { // permute colnames by S->q :  cn <- cn[ S->q ] :
		SEXP cn = PROTECT(duplicate(VECTOR_ELT(dn, 1)));
		for(int j=0; j < n; j++)
		    SET_STRING_ELT(VECTOR_ELT(dn, 1), j, STRING_ELT(cn, S->q[j]));
		UNPROTECT(1); // cn
	    }
	    SET_VECTOR_ELT(dn, 0, R_NilValue); // rownames(.) := NULL
	}
    }
    SET_SLOT(ans, Matrix_USym,
	     Matrix_cs_to_SEXP(N->U, "dtCMatrix", 0, do_dn ? dn : R_NilValue));
    if(do_dn) UNPROTECT(1); // dn
    Memcpy(INTEGER(ALLOC_SLOT(ans, Matrix_pSym, /* "p" */
			      INTSXP, n)), p, n);
    if (order)
	Memcpy(INTEGER(ALLOC_SLOT(ans, install("q"),
				  INTSXP, n)), S->q, n);
    cs_nfree(N);
    cs_sfree(S);
    cs_free(p);
    UNPROTECT(1);
    set_factors(Ap, ans, "LU");
}

SEXP dgCMatrix_LU(SEXP Ap, SEXP orderp, SEXP tolp, SEXP error_on_sing, SEXP keep_dimnames)
{
    SEXP ans;
    Rboolean err_sing = asLogical(error_on_sing);
    /* FIXME: dgCMatrix_LU should check ans for consistency in
     * permutation type with the requested value - Should have two
     * classes or two different names in the factors list for LU with
     * permuted columns or not.
     * OTOH, currently  (order, tol) === (1, 1) always.
     * It is true that length(LU@q) does flag the order argument.
     */
    if (!isNull(ans = get_factors(Ap, "LU")))
	return ans;
    int keep_dimnms = asLogical(keep_dimnames);
    if(keep_dimnms == NA_LOGICAL) { keep_dimnms = TRUE;
	warning(_("dgcMatrix_LU(*, keep_dimnames = NA): NA taken as TRUE"));
    }
    install_lu(Ap, asInteger(orderp), asReal(tolp), err_sing, keep_dimnms);
    return get_factors(Ap, "LU");
}

SEXP dgCMatrix_matrix_solve(SEXP Ap, SEXP b, SEXP give_sparse)
// FIXME:  add  'keep_dimnames' as argument
{
    Rboolean sparse = asLogical(give_sparse);
    if(sparse) {
	// FIXME: implement this
	error(_("dgCMatrix_matrix_solve(.., sparse=TRUE) not yet implemented"));

	/* Idea: in the  for(j = 0; j < nrhs ..) loop below, build the *sparse* result matrix
	 * ----- *column* wise -- which is perfect for dgCMatrix
	 * --> build (i,p,x) slots "increasingly" [well, allocate in batches ..]
	 *
	 * --> maybe first a protoype in R
	 */

    }
    SEXP ans = PROTECT(dup_mMatrix_as_dgeMatrix(b)),
	lu, qslot;
    CSP L, U;
    int *bdims = INTEGER(GET_SLOT(ans, Matrix_DimSym)), *p, *q;
    int j, n = bdims[0], nrhs = bdims[1];
    double *x, *ax = REAL(GET_SLOT(ans, Matrix_xSym));
    C_or_Alloca_TO(x, n, double);

    if (isNull(lu = get_factors(Ap, "LU"))) {
	install_lu(Ap, /* order = */ 1, /* tol = */ 1.0, /* err_sing = */ TRUE,
		   /* keep_dimnames = */ TRUE);
	lu = get_factors(Ap, "LU");
    }
    qslot = GET_SLOT(lu, install("q"));
    L = AS_CSP__(GET_SLOT(lu, Matrix_LSym));
    U = AS_CSP__(GET_SLOT(lu, Matrix_USym));
    R_CheckStack();
    if (U->n != n)
	error(_("Dimensions of system to be solved are inconsistent"));
    if(nrhs >= 1 && n >= 1) {
	p = INTEGER(GET_SLOT(lu, Matrix_pSym));
	q = LENGTH(qslot) ? INTEGER(qslot) : (int *) NULL;

	for (j = 0; j < nrhs; j++) {
	    cs_pvec(p, ax + j * n, x, n);  /* x = b(p) */
	    cs_lsolve(L, x);	       /* x = L\x */
	    cs_usolve(U, x);	       /* x = U\x */
	    if (q)		       /* r(q) = x , hence
					  r = Q' U{^-1} L{^-1} P b = A^{-1} b */
		cs_ipvec(q, x, ax + j * n, n);
	    else
		Memcpy(ax + j * n, x, n);
	}
    }
    if(n >= SMALL_4_Alloca) Free(x);
    UNPROTECT(1);
    return ans;
}

// called from package MatrixModels's R code:
SEXP dgCMatrix_cholsol(SEXP x, SEXP y)
{
    /* Solve Sparse Least Squares X %*% beta ~= y  with dense RHS y,
     * where X = t(x) i.e. we pass  x = t(X)  as argument,
     * via  "Cholesky(X'X)" .. well not really:
     * cholmod_factorize("x", ..) finds L in  X'X = L'L directly */
    CHM_SP cx = AS_CHM_SP(x);
    /* FIXME: extend this to work in multivariate case, i.e. y a matrix with > 1 column ! */
    SEXP y_ = PROTECT(coerceVector(y, REALSXP));
    CHM_DN cy = AS_CHM_DN(y_), rhs, cAns, resid;
    CHM_FR L;
    int n = cx->ncol;/* #{obs.} {x = t(X) !} */
    double one[] = {1,0}, zero[] = {0,0}, neg1[] = {-1,0};
    const char *nms[] = {"L", "coef", "Xty", "resid", ""};
    SEXP ans = PROTECT(Rf_mkNamed(VECSXP, nms));
    R_CheckStack();

    if (n < cx->nrow || n <= 0)
	error(_("dgCMatrix_cholsol requires a 'short, wide' rectangular matrix"));
    if (cy->nrow != n)
	error(_("Dimensions of system to be solved are inconsistent"));
    rhs = cholmod_allocate_dense(cx->nrow, 1, cx->nrow, CHOLMOD_REAL, &c);
    /* cholmod_sdmult(A, transp, alpha, beta, X, Y, &c):
     *		Y := alpha*(A*X) + beta*Y or alpha*(A'*X) + beta*Y ;
     * here: rhs := 1 * x %*% y + 0 =  x %*% y =  X'y  */
    if (!(cholmod_sdmult(cx, 0 /* trans */, one, zero, cy, rhs, &c)))
	error(_("cholmod_sdmult error (rhs)"));
    L = cholmod_analyze(cx, &c);
    if (!cholmod_factorize(cx, L, &c))
	error(_("cholmod_factorize failed: status %d, minor %d from ncol %d"),
	      c.status, L->minor, L->n);
/* FIXME: Do this in stages so an "effects" vector can be calculated */
    if (!(cAns = cholmod_solve(CHOLMOD_A, L, rhs, &c)))
	error(_("cholmod_solve (CHOLMOD_A) failed: status %d, minor %d from ncol %d"),
	      c.status, L->minor, L->n);
    /* L : */
    SET_VECTOR_ELT(ans, 0, chm_factor_to_SEXP(L, 0));
    /* coef : */
    SET_VECTOR_ELT(ans, 1, allocVector(REALSXP, cx->nrow));
    Memcpy(REAL(VECTOR_ELT(ans, 1)), (double*)(cAns->x), cx->nrow);
    /* X'y : */
/* FIXME: Change this when the "effects" vector is available */
    SET_VECTOR_ELT(ans, 2, allocVector(REALSXP, cx->nrow));
    Memcpy(REAL(VECTOR_ELT(ans, 2)), (double*)(rhs->x), cx->nrow);
    /* resid := y */
    resid = cholmod_copy_dense(cy, &c);
    /* cholmod_sdmult(A, transp, alp, bet, X, Y, &c):
     *		Y := alp*(A*X) + bet*Y or alp*(A'*X) + beta*Y ;
     * here: resid := -1 * x' %*% coef + 1 * y = y - X %*% coef  */
    if (!(cholmod_sdmult(cx, 1/* trans */, neg1, one, cAns, resid, &c)))
	error(_("cholmod_sdmult error (resid)"));
    /* FIXME: for multivariate case, i.e. resid  *matrix* with > 1 column ! */
    SET_VECTOR_ELT(ans, 3, allocVector(REALSXP, n));
    Memcpy(REAL(VECTOR_ELT(ans, 3)), (double*)(resid->x), n);

    cholmod_free_factor(&L, &c);
    cholmod_free_dense(&rhs, &c);
    cholmod_free_dense(&cAns, &c);
    UNPROTECT(2);
    return ans;
}


/* Define all of
 *  dgCMatrix_colSums(....)
 *  igCMatrix_colSums(....)
 *  lgCMatrix_colSums_d(....)
 *  lgCMatrix_colSums_i(....)
 *  ngCMatrix_colSums_d(....)
 *  ngCMatrix_colSums_i(....)
 */
#define _dgC_
#include "t_gCMatrix_colSums.c"

#define _igC_
#include "t_gCMatrix_colSums.c"

#define _lgC_
#include "t_gCMatrix_colSums.c"

#define _ngC_
#include "t_gCMatrix_colSums.c"

#define _lgC_mn
#include "t_gCMatrix_colSums.c"

#define _ngC_mn
#include "t_gCMatrix_colSums.c"


SEXP lgCMatrix_colSums(SEXP x, SEXP NArm, SEXP spRes, SEXP trans, SEXP means)
{
    if(asLogical(means)) /* ==> result will be "double" / "dsparseVector" */
	return lgCMatrix_colSums_d(x, NArm, spRes, trans, means);
    else
	return lgCMatrix_colSums_i(x, NArm, spRes, trans, means);
}

SEXP ngCMatrix_colSums(SEXP x, SEXP NArm, SEXP spRes, SEXP trans, SEXP means)
{
    if(asLogical(means)) /* ==> result will be "double" / "dsparseVector" */
	return ngCMatrix_colSums_d(x, NArm, spRes, trans, means);
    else
	return ngCMatrix_colSums_i(x, NArm, spRes, trans, means);
}
