zstedc.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

#include "blaswrap.h"
/*  -- translated by f2c (version 19990503).
   You must link the resulting object file with the libraries:
	-lf2c -lm   (in that order)
*/

#include "f2c.h"

/* Common Block Declarations */

struct {
    doublereal ops, itcnt;
} latime_;

#define latime_1 latime_

/* Table of constant values */

static integer c__2 = 2;
static integer c__9 = 9;
static integer c__0 = 0;
static doublereal c_b18 = 0.;
static doublereal c_b19 = 1.;
static integer c__1 = 1;

/* Subroutine */ int zstedc_(char *compz, integer *n, doublereal *d__, 
	doublereal *e, doublecomplex *z__, integer *ldz, doublecomplex *work, 
	integer *lwork, doublereal *rwork, integer *lrwork, integer *iwork, 
	integer *liwork, integer *info)
{
    /* System generated locals */
    integer z_dim1, z_offset, i__1, i__2, i__3, i__4;
    doublereal d__1, d__2;

    /* Builtin functions */
    double log(doublereal);
    integer pow_ii(integer *, integer *);
    double sqrt(doublereal);

    /* Local variables */
    static doublereal tiny;
    static integer i__, j, k, m;
    static doublereal p;
    extern logical lsame_(char *, char *);
    static integer lwmin, start;
    extern /* Subroutine */ int zswap_(integer *, doublecomplex *, integer *, 
	    doublecomplex *, integer *), zlaed0_(integer *, integer *, 
	    doublereal *, doublereal *, doublecomplex *, integer *, 
	    doublecomplex *, integer *, doublereal *, integer *, integer *);
    static integer ii, ll;
    extern doublereal dlamch_(char *);
    extern /* Subroutine */ int dlascl_(char *, integer *, integer *, 
	    doublereal *, doublereal *, integer *, integer *, doublereal *, 
	    integer *, integer *), dstedc_(char *, integer *, 
	    doublereal *, doublereal *, doublereal *, integer *, doublereal *,
	     integer *, integer *, integer *, integer *), dlaset_(
	    char *, integer *, integer *, doublereal *, doublereal *, 
	    doublereal *, integer *), xerbla_(char *, integer *);
    extern integer ilaenv_(integer *, char *, char *, integer *, integer *, 
	    integer *, integer *, ftnlen, ftnlen);
    extern doublereal dlanst_(char *, integer *, doublereal *, doublereal *);
    extern /* Subroutine */ int dsterf_(integer *, doublereal *, doublereal *,
	     integer *), zlacrm_(integer *, integer *, doublecomplex *, 
	    integer *, doublereal *, integer *, doublecomplex *, integer *, 
	    doublereal *);
    static integer liwmin, icompz;
    extern /* Subroutine */ int dsteqr_(char *, integer *, doublereal *, 
	    doublereal *, doublereal *, integer *, doublereal *, integer *), zlacpy_(char *, integer *, integer *, doublecomplex *, 
	    integer *, doublecomplex *, integer *);
    static doublereal orgnrm;
    static integer lrwmin;
    static logical lquery;
    static integer smlsiz;
    extern /* Subroutine */ int zsteqr_(char *, integer *, doublereal *, 
	    doublereal *, doublecomplex *, integer *, doublereal *, integer *);
    static integer end, lgn;
    static doublereal eps;


#define z___subscr(a_1,a_2) (a_2)*z_dim1 + a_1
#define z___ref(a_1,a_2) z__[z___subscr(a_1,a_2)]


/*  -- LAPACK routine (instrumented to count operations, version 3.0) --   
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
       Courant Institute, Argonne National Lab, and Rice University   
       June 30, 1999   

       Common block to return operation count and iteration count   
       ITCNT is initialized to 0, OPS is only incremented   

    Purpose   
    =======   

    ZSTEDC computes all eigenvalues and, optionally, eigenvectors of a   
    symmetric tridiagonal matrix using the divide and conquer method.   
    The eigenvectors of a full or band complex Hermitian matrix can also   
    be found if ZHETRD or ZHPTRD or ZHBTRD has been used to reduce this   
    matrix to tridiagonal form.   

    This code makes very mild assumptions about floating point   
    arithmetic. It will work on machines with a guard digit in   
    add/subtract, or on those binary machines without guard digits   
    which subtract like the Cray X-MP, Cray Y-MP, Cray C-90, or Cray-2.   
    It could conceivably fail on hexadecimal or decimal machines   
    without guard digits, but we know of none.  See DLAED3 for details.   

    Arguments   
    =========   

    COMPZ   (input) CHARACTER*1   
            = 'N':  Compute eigenvalues only.   
            = 'I':  Compute eigenvectors of tridiagonal matrix also.   
            = 'V':  Compute eigenvectors of original Hermitian matrix   
                    also.  On entry, Z contains the unitary matrix used   
                    to reduce the original matrix to tridiagonal form.   

    N       (input) INTEGER   
            The dimension of the symmetric tridiagonal matrix.  N >= 0.   

    D       (input/output) DOUBLE PRECISION array, dimension (N)   
            On entry, the diagonal elements of the tridiagonal matrix.   
            On exit, if INFO = 0, the eigenvalues in ascending order.   

    E       (input/output) DOUBLE PRECISION array, dimension (N-1)   
            On entry, the subdiagonal elements of the tridiagonal matrix.   
            On exit, E has been destroyed.   

    Z       (input/output) COMPLEX*16 array, dimension (LDZ,N)   
            On entry, if COMPZ = 'V', then Z contains the unitary   
            matrix used in the reduction to tridiagonal form.   
            On exit, if INFO = 0, then if COMPZ = 'V', Z contains the   
            orthonormal eigenvectors of the original Hermitian matrix,   
            and if COMPZ = 'I', Z contains the orthonormal eigenvectors   
            of the symmetric tridiagonal matrix.   
            If  COMPZ = 'N', then Z is not referenced.   

    LDZ     (input) INTEGER   
            The leading dimension of the array Z.  LDZ >= 1.   
            If eigenvectors are desired, then LDZ >= max(1,N).   

    WORK    (workspace/output) COMPLEX*16 array, dimension (LWORK)   
            On exit, if INFO = 0, WORK(1) returns the optimal LWORK.   

    LWORK   (input) INTEGER   
            The dimension of the array WORK.   
            If COMPZ = 'N' or 'I', or N <= 1, LWORK must be at least 1.   
            If COMPZ = 'V' and N > 1, LWORK must be at least N*N.   

            If LWORK = -1, then a workspace query is assumed; the routine   
            only calculates the optimal size of the WORK array, returns   
            this value as the first entry of the WORK array, and no error   
            message related to LWORK is issued by XERBLA.   

    RWORK   (workspace/output) DOUBLE PRECISION array,   
                                           dimension (LRWORK)   
            On exit, if INFO = 0, RWORK(1) returns the optimal LRWORK.   

    LRWORK  (input) INTEGER   
            The dimension of the array RWORK.   
            If COMPZ = 'N' or N <= 1, LRWORK must be at least 1.   
            If COMPZ = 'V' and N > 1, LRWORK must be at least   
                           1 + 3*N + 2*N*lg N + 3*N**2 ,   
                           where lg( N ) = smallest integer k such   
                           that 2**k >= N.   
            If COMPZ = 'I' and N > 1, LRWORK must be at least   
                           1 + 4*N + 2*N**2 .   

            If LRWORK = -1, then a workspace query is assumed; the   
            routine only calculates the optimal size of the RWORK array,   
            returns this value as the first entry of the RWORK array, and   
            no error message related to LRWORK is issued by XERBLA.   

    IWORK   (workspace/output) INTEGER array, dimension (LIWORK)   
            On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.   

    LIWORK  (input) INTEGER   
            The dimension of the array IWORK.   
            If COMPZ = 'N' or N <= 1, LIWORK must be at least 1.   
            If COMPZ = 'V' or N > 1,  LIWORK must be at least   
                                      6 + 6*N + 5*N*lg N.   
            If COMPZ = 'I' or N > 1,  LIWORK must be at least   
                                      3 + 5*N .   

            If LIWORK = -1, then a workspace query is assumed; the   
            routine only calculates the optimal size of the IWORK array,   
            returns this value as the first entry of the IWORK array, and   
            no error message related to LIWORK is issued by XERBLA.   

    INFO    (output) INTEGER   
            = 0:  successful exit.   
            < 0:  if INFO = -i, the i-th argument had an illegal value.   
            > 0:  The algorithm failed to compute an eigenvalue while   
                  working on the submatrix lying in rows and columns   
                  INFO/(N+1) through mod(INFO,N+1).   

    Further Details   
    ===============   

    Based on contributions by   
       Jeff Rutter, Computer Science Division, University of California   
       at Berkeley, USA   

    =====================================================================   


       Test the input parameters.   

       Parameter adjustments */
    --d__;
    --e;
    z_dim1 = *ldz;
    z_offset = 1 + z_dim1 * 1;
    z__ -= z_offset;
    --work;
    --rwork;
    --iwork;

    /* Function Body */
    *info = 0;
    lquery = *lwork == -1 || *lrwork == -1 || *liwork == -1;

    if (lsame_(compz, "N")) {
	icompz = 0;
    } else if (lsame_(compz, "V")) {
	icompz = 1;
    } else if (lsame_(compz, "I")) {
	icompz = 2;
    } else {
	icompz = -1;
    }
    if (*n <= 1 || icompz <= 0) {
	lwmin = 1;
	liwmin = 1;
	lrwmin = 1;
    } else {
	lgn = (integer) (log((doublereal) (*n)) / log(2.));
	if (pow_ii(&c__2, &lgn) < *n) {
	    ++lgn;
	}
	if (pow_ii(&c__2, &lgn) < *n) {
	    ++lgn;
	}
	if (icompz == 1) {