dlalsd.c

著名的LAPACK矩阵计算软件包, 是比较新的版本, 一般用到矩阵分解的朋友也许会用到

		i__2 = *n - 1;
		for (j = 1; j <= i__2; ++j) {
		    cs = work[(j << 1) - 1];
		    sn = work[j * 2];
		    drot_(&c__1, &b_ref(j, i__), &c__1, &b_ref(j + 1, i__), &
			    c__1, &cs, &sn);
/* L20: */
		}
/* L30: */
	    }
	}
    }

/*     Scale. */

    nm1 = *n - 1;
    orgnrm = dlanst_("M", n, &d__[1], &e[1]);
    if (orgnrm == 0.) {
	dlaset_("A", n, nrhs, &c_b6, &c_b6, &b[b_offset], ldb);
	return 0;
    }

    latime_1.ops += (doublereal) (*n + nm1);
    dlascl_("G", &c__0, &c__0, &orgnrm, &c_b11, n, &c__1, &d__[1], n, info);
    dlascl_("G", &c__0, &c__0, &orgnrm, &c_b11, &nm1, &c__1, &e[1], &nm1, 
	    info);

/*     If N is smaller than the minimum divide size SMLSIZ, then solve   
       the problem with another solver. */

    if (*n <= *smlsiz) {
	nwork = *n * *n + 1;
	dlaset_("A", n, n, &c_b6, &c_b11, &work[1], n);
	dlasdq_("U", &c__0, n, n, &c__0, nrhs, &d__[1], &e[1], &work[1], n, &
		work[1], n, &b[b_offset], ldb, &work[nwork], info);
	if (*info != 0) {
	    return 0;
	}
	latime_1.ops += 1.;
	tol = *rcond * (d__1 = d__[idamax_(n, &d__[1], &c__1)], abs(d__1));
	i__1 = *n;
	for (i__ = 1; i__ <= i__1; ++i__) {
	    if (d__[i__] <= tol) {
		dlaset_("A", &c__1, nrhs, &c_b6, &c_b6, &b_ref(i__, 1), ldb);
	    } else {
		latime_1.ops += (doublereal) (*nrhs);
		dlascl_("G", &c__0, &c__0, &d__[i__], &c_b11, &c__1, nrhs, &
			b_ref(i__, 1), ldb, info);
		++(*rank);
	    }
/* L40: */
	}
	latime_1.ops += dopbl3_("DGEMM ", n, nrhs, n);
	dgemm_("T", "N", n, nrhs, n, &c_b11, &work[1], n, &b[b_offset], ldb, &
		c_b6, &work[nwork], n);
	dlacpy_("A", n, nrhs, &work[nwork], n, &b[b_offset], ldb);

/*        Unscale. */

	latime_1.ops += (doublereal) (*n + *n * *nrhs);
	dlascl_("G", &c__0, &c__0, &c_b11, &orgnrm, n, &c__1, &d__[1], n, 
		info);
	dlasrt_("D", n, &d__[1], info);
	dlascl_("G", &c__0, &c__0, &orgnrm, &c_b11, n, nrhs, &b[b_offset], 
		ldb, info);

	return 0;
    }

/*     Book-keeping and setting up some constants. */

    nlvl = (integer) (log((doublereal) (*n) / (doublereal) (*smlsiz + 1)) / 
	    log(2.)) + 1;

    smlszp = *smlsiz + 1;

    u = 1;
    vt = *smlsiz * *n + 1;
    difl = vt + smlszp * *n;
    difr = difl + nlvl * *n;
    z__ = difr + (nlvl * *n << 1);
    c__ = z__ + nlvl * *n;
    s = c__ + *n;
    poles = s + *n;
    givnum = poles + (nlvl << 1) * *n;
    bx = givnum + (nlvl << 1) * *n;
    nwork = bx + *n * *nrhs;

    sizei = *n + 1;
    k = sizei + *n;
    givptr = k + *n;
    perm = givptr + *n;
    givcol = perm + nlvl * *n;
    iwk = givcol + (nlvl * *n << 1);

    st = 1;
    sqre = 0;
    icmpq1 = 1;
    icmpq2 = 0;
    nsub = 0;

    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {
	if ((d__1 = d__[i__], abs(d__1)) < eps) {
	    d__[i__] = d_sign(&eps, &d__[i__]);
	}
/* L50: */
    }

    i__1 = nm1;
    for (i__ = 1; i__ <= i__1; ++i__) {
	if ((d__1 = e[i__], abs(d__1)) < eps || i__ == nm1) {
	    ++nsub;
	    iwork[nsub] = st;

/*           Subproblem found. First determine its size and then   
             apply divide and conquer on it. */

	    if (i__ < nm1) {

/*              A subproblem with E(I) small for I < NM1. */

		nsize = i__ - st + 1;
		iwork[sizei + nsub - 1] = nsize;
	    } else if ((d__1 = e[i__], abs(d__1)) >= eps) {

/*              A subproblem with E(NM1) not too small but I = NM1. */

		nsize = *n - st + 1;
		iwork[sizei + nsub - 1] = nsize;
	    } else {

/*              A subproblem with E(NM1) small. This implies an   
                1-by-1 subproblem at D(N), which is not solved   
                explicitly. */

		nsize = i__ - st + 1;
		iwork[sizei + nsub - 1] = nsize;
		++nsub;
		iwork[nsub] = *n;
		iwork[sizei + nsub - 1] = 1;
		dcopy_(nrhs, &b_ref(*n, 1), ldb, &work[bx + nm1], n);
	    }
	    st1 = st - 1;
	    if (nsize == 1) {

/*              This is a 1-by-1 subproblem and is not solved   
                explicitly. */

		dcopy_(nrhs, &b_ref(st, 1), ldb, &work[bx + st1], n);
	    } else if (nsize <= *smlsiz) {

/*              This is a small subproblem and is solved by DLASDQ. */

		dlaset_("A", &nsize, &nsize, &c_b6, &c_b11, &work[vt + st1], 
			n);
		dlasdq_("U", &c__0, &nsize, &nsize, &c__0, nrhs, &d__[st], &e[
			st], &work[vt + st1], n, &work[nwork], n, &b_ref(st, 
			1), ldb, &work[nwork], info);
		if (*info != 0) {
		    return 0;
		}
		dlacpy_("A", &nsize, nrhs, &b_ref(st, 1), ldb, &work[bx + st1]
			, n);
	    } else {

/*              A large problem. Solve it using divide and conquer. */

		dlasda_(&icmpq1, smlsiz, &nsize, &sqre, &d__[st], &e[st], &
			work[u + st1], n, &work[vt + st1], &iwork[k + st1], &
			work[difl + st1], &work[difr + st1], &work[z__ + st1],
			 &work[poles + st1], &iwork[givptr + st1], &iwork[
			givcol + st1], n, &iwork[perm + st1], &work[givnum + 
			st1], &work[c__ + st1], &work[s + st1], &work[nwork], 
			&iwork[iwk], info);
		if (*info != 0) {
		    return 0;
		}
		bxst = bx + st1;
		dlalsa_(&icmpq2, smlsiz, &nsize, nrhs, &b_ref(st, 1), ldb, &
			work[bxst], n, &work[u + st1], n, &work[vt + st1], &
			iwork[k + st1], &work[difl + st1], &work[difr + st1], 
			&work[z__ + st1], &work[poles + st1], &iwork[givptr + 
			st1], &iwork[givcol + st1], n, &iwork[perm + st1], &
			work[givnum + st1], &work[c__ + st1], &work[s + st1], 
			&work[nwork], &iwork[iwk], info);
		if (*info != 0) {
		    return 0;
		}
	    }
	    st = i__ + 1;
	}
/* L60: */
    }

/*     Apply the singular values and treat the tiny ones as zero. */

    tol = *rcond * (d__1 = d__[idamax_(n, &d__[1], &c__1)], abs(d__1));

    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {

/*        Some of the elements in D can be negative because 1-by-1   
          subproblems were not solved explicitly. */

	if ((d__1 = d__[i__], abs(d__1)) <= tol) {
	    dlaset_("A", &c__1, nrhs, &c_b6, &c_b6, &work[bx + i__ - 1], n);
	} else {
	    ++(*rank);
	    latime_1.ops += (doublereal) (*nrhs);
	    dlascl_("G", &c__0, &c__0, &d__[i__], &c_b11, &c__1, nrhs, &work[
		    bx + i__ - 1], n, info);
	}
	d__[i__] = (d__1 = d__[i__], abs(d__1));
/* L70: */
    }

/*     Now apply back the right singular vectors. */

    icmpq2 = 1;
    i__1 = nsub;
    for (i__ = 1; i__ <= i__1; ++i__) {
	st = iwork[i__];
	st1 = st - 1;
	nsize = iwork[sizei + i__ - 1];
	bxst = bx + st1;
	if (nsize == 1) {
	    dcopy_(nrhs, &work[bxst], n, &b_ref(st, 1), ldb);
	} else if (nsize <= *smlsiz) {
	    latime_1.ops += dopbl3_("DGEMM ", &nsize, nrhs, &nsize)
		    ;
	    dgemm_("T", "N", &nsize, nrhs, &nsize, &c_b11, &work[vt + st1], n,
		     &work[bxst], n, &c_b6, &b_ref(st, 1), ldb);
	} else {
	    dlalsa_(&icmpq2, smlsiz, &nsize, nrhs, &work[bxst], n, &b_ref(st, 
		    1), ldb, &work[u + st1], n, &work[vt + st1], &iwork[k + 
		    st1], &work[difl + st1], &work[difr + st1], &work[z__ + 
		    st1], &work[poles + st1], &iwork[givptr + st1], &iwork[
		    givcol + st1], n, &iwork[perm + st1], &work[givnum + st1],
		     &work[c__ + st1], &work[s + st1], &work[nwork], &iwork[
		    iwk], info);
	    if (*info != 0) {
		return 0;
	    }
	}
/* L80: */
    }

/*     Unscale and sort the singular values. */

    latime_1.ops += (doublereal) (*n + *n * *nrhs);
    dlascl_("G", &c__0, &c__0, &c_b11, &orgnrm, n, &c__1, &d__[1], n, info);
    dlasrt_("D", n, &d__[1], info);
    dlascl_("G", &c__0, &c__0, &orgnrm, &c_b11, n, nrhs, &b[b_offset], ldb, 
	    info);

    return 0;

/*     End of DLALSD */

} /* dlalsd_ */

#undef b_ref