Exemplo n.º 1
0
/* Subroutine */ int ssytrd_(char *uplo, integer *n, real *a, integer *lda,
                             real *d__, real *e, real *tau, real *work, integer *lwork, integer *
                             info)
{
    /* System generated locals */
    integer a_dim1, a_offset, i__1, i__2, i__3;

    /* Local variables */
    integer i__, j, nb, kk, nx, iws;
    extern logical lsame_(char *, char *);
    integer nbmin, iinfo;
    logical upper;
    extern /* Subroutine */ int ssytd2_(char *, integer *, real *, integer *,
                                        real *, real *, real *, integer *), ssyr2k_(char *, char *
                                                , integer *, integer *, real *, real *, integer *, real *,
                                                integer *, real *, real *, integer *), xerbla_(
                                                        char *, integer *);
    extern integer ilaenv_(integer *, char *, char *, integer *, integer *,
                           integer *, integer *);
    extern /* Subroutine */ int slatrd_(char *, integer *, integer *, real *,
                                        integer *, real *, real *, real *, integer *);
    integer ldwork, lwkopt;
    logical lquery;


    /*  -- LAPACK routine (version 3.2) -- */
    /*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
    /*     November 2006 */

    /*     .. Scalar Arguments .. */
    /*     .. */
    /*     .. Array Arguments .. */
    /*     .. */

    /*  Purpose */
    /*  ======= */

    /*  SSYTRD reduces a real symmetric matrix A to real symmetric */
    /*  tridiagonal form T by an orthogonal similarity transformation: */
    /*  Q**T * A * Q = T. */

    /*  Arguments */
    /*  ========= */

    /*  UPLO    (input) CHARACTER*1 */
    /*          = 'U':  Upper triangle of A is stored; */
    /*          = 'L':  Lower triangle of A is stored. */

    /*  N       (input) INTEGER */
    /*          The order of the matrix A.  N >= 0. */

    /*  A       (input/output) REAL array, dimension (LDA,N) */
    /*          On entry, the symmetric matrix A.  If UPLO = 'U', the leading */
    /*          N-by-N upper triangular part of A contains the upper */
    /*          triangular part of the matrix A, and the strictly lower */
    /*          triangular part of A is not referenced.  If UPLO = 'L', the */
    /*          leading N-by-N lower triangular part of A contains the lower */
    /*          triangular part of the matrix A, and the strictly upper */
    /*          triangular part of A is not referenced. */
    /*          On exit, if UPLO = 'U', the diagonal and first superdiagonal */
    /*          of A are overwritten by the corresponding elements of the */
    /*          tridiagonal matrix T, and the elements above the first */
    /*          superdiagonal, with the array TAU, represent the orthogonal */
    /*          matrix Q as a product of elementary reflectors; if UPLO */
    /*          = 'L', the diagonal and first subdiagonal of A are over- */
    /*          written by the corresponding elements of the tridiagonal */
    /*          matrix T, and the elements below the first subdiagonal, with */
    /*          the array TAU, represent the orthogonal matrix Q as a product */
    /*          of elementary reflectors. See Further Details. */

    /*  LDA     (input) INTEGER */
    /*          The leading dimension of the array A.  LDA >= max(1,N). */

    /*  D       (output) REAL array, dimension (N) */
    /*          The diagonal elements of the tridiagonal matrix T: */
    /*          D(i) = A(i,i). */

    /*  E       (output) REAL array, dimension (N-1) */
    /*          The off-diagonal elements of the tridiagonal matrix T: */
    /*          E(i) = A(i,i+1) if UPLO = 'U', E(i) = A(i+1,i) if UPLO = 'L'. */

    /*  TAU     (output) REAL array, dimension (N-1) */
    /*          The scalar factors of the elementary reflectors (see Further */
    /*          Details). */

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

    /*  LWORK   (input) INTEGER */
    /*          The dimension of the array WORK.  LWORK >= 1. */
    /*          For optimum performance LWORK >= N*NB, where NB is the */
    /*          optimal blocksize. */

    /*          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. */

    /*  INFO    (output) INTEGER */
    /*          = 0:  successful exit */
    /*          < 0:  if INFO = -i, the i-th argument had an illegal value */

    /*  Further Details */
    /*  =============== */

    /*  If UPLO = 'U', the matrix Q is represented as a product of elementary */
    /*  reflectors */

    /*     Q = H(n-1) . . . H(2) H(1). */

    /*  Each H(i) has the form */

    /*     H(i) = I - tau * v * v' */

    /*  where tau is a real scalar, and v is a real vector with */
    /*  v(i+1:n) = 0 and v(i) = 1; v(1:i-1) is stored on exit in */
    /*  A(1:i-1,i+1), and tau in TAU(i). */

    /*  If UPLO = 'L', the matrix Q is represented as a product of elementary */
    /*  reflectors */

    /*     Q = H(1) H(2) . . . H(n-1). */

    /*  Each H(i) has the form */

    /*     H(i) = I - tau * v * v' */

    /*  where tau is a real scalar, and v is a real vector with */
    /*  v(1:i) = 0 and v(i+1) = 1; v(i+2:n) is stored on exit in A(i+2:n,i), */
    /*  and tau in TAU(i). */

    /*  The contents of A on exit are illustrated by the following examples */
    /*  with n = 5: */

    /*  if UPLO = 'U':                       if UPLO = 'L': */

    /*    (  d   e   v2  v3  v4 )              (  d                  ) */
    /*    (      d   e   v3  v4 )              (  e   d              ) */
    /*    (          d   e   v4 )              (  v1  e   d          ) */
    /*    (              d   e  )              (  v1  v2  e   d      ) */
    /*    (                  d  )              (  v1  v2  v3  e   d  ) */

    /*  where d and e denote diagonal and off-diagonal elements of T, and vi */
    /*  denotes an element of the vector defining H(i). */

    /*  ===================================================================== */

    /*     .. Parameters .. */
    /*     .. */
    /*     .. Local Scalars .. */
    /*     .. */
    /*     .. External Subroutines .. */
    /*     .. */
    /*     .. Intrinsic Functions .. */
    /*     .. */
    /*     .. External Functions .. */
    /*     .. */
    /*     .. Executable Statements .. */

    /*     Test the input parameters */

    /* Parameter adjustments */
    a_dim1 = *lda;
    a_offset = 1 + a_dim1;
    a -= a_offset;
    --d__;
    --e;
    --tau;
    --work;

    /* Function Body */
    *info = 0;
    upper = lsame_(uplo, "U");
    lquery = *lwork == -1;
    if (! upper && ! lsame_(uplo, "L")) {
        *info = -1;
    } else if (*n < 0) {
        *info = -2;
    } else if (*lda < max(1,*n)) {
        *info = -4;
    } else if (*lwork < 1 && ! lquery) {
        *info = -9;
    }

    if (*info == 0) {

        /*        Determine the block size. */

        nb = ilaenv_(&c__1, "SSYTRD", uplo, n, &c_n1, &c_n1, &c_n1);
        lwkopt = *n * nb;
        work[1] = (real) lwkopt;
    }

    if (*info != 0) {
        i__1 = -(*info);
        xerbla_("SSYTRD", &i__1);
        return 0;
    } else if (lquery) {
        return 0;
    }

    /*     Quick return if possible */

    if (*n == 0) {
        work[1] = 1.f;
        return 0;
    }

    nx = *n;
    iws = 1;
    if (nb > 1 && nb < *n) {

        /*        Determine when to cross over from blocked to unblocked code */
        /*        (last block is always handled by unblocked code). */

        /* Computing MAX */
        i__1 = nb, i__2 = ilaenv_(&c__3, "SSYTRD", uplo, n, &c_n1, &c_n1, &
                                  c_n1);
        nx = max(i__1,i__2);
        if (nx < *n) {

            /*           Determine if workspace is large enough for blocked code. */

            ldwork = *n;
            iws = ldwork * nb;
            if (*lwork < iws) {

                /*              Not enough workspace to use optimal NB:  determine the */
                /*              minimum value of NB, and reduce NB or force use of */
                /*              unblocked code by setting NX = N. */

                /* Computing MAX */
                i__1 = *lwork / ldwork;
                nb = max(i__1,1);
                nbmin = ilaenv_(&c__2, "SSYTRD", uplo, n, &c_n1, &c_n1, &c_n1);
                if (nb < nbmin) {
                    nx = *n;
                }
            }
        } else {
            nx = *n;
        }
    } else {
        nb = 1;
    }

    if (upper) {

        /*        Reduce the upper triangle of A. */
        /*        Columns 1:kk are handled by the unblocked method. */

        kk = *n - (*n - nx + nb - 1) / nb * nb;
        i__1 = kk + 1;
        i__2 = -nb;
        for (i__ = *n - nb + 1; i__2 < 0 ? i__ >= i__1 : i__ <= i__1; i__ +=
                    i__2) {

            /*           Reduce columns i:i+nb-1 to tridiagonal form and form the */
            /*           matrix W which is needed to update the unreduced part of */
            /*           the matrix */

            i__3 = i__ + nb - 1;
            slatrd_(uplo, &i__3, &nb, &a[a_offset], lda, &e[1], &tau[1], &
                    work[1], &ldwork);

            /*           Update the unreduced submatrix A(1:i-1,1:i-1), using an */
            /*           update of the form:  A := A - V*W' - W*V' */

            i__3 = i__ - 1;
            ssyr2k_(uplo, "No transpose", &i__3, &nb, &c_b22, &a[i__ * a_dim1
                    + 1], lda, &work[1], &ldwork, &c_b23, &a[a_offset], lda);

            /*           Copy superdiagonal elements back into A, and diagonal */
            /*           elements into D */

            i__3 = i__ + nb - 1;
            for (j = i__; j <= i__3; ++j) {
                a[j - 1 + j * a_dim1] = e[j - 1];
                d__[j] = a[j + j * a_dim1];
                /* L10: */
            }
            /* L20: */
        }

        /*        Use unblocked code to reduce the last or only block */

        ssytd2_(uplo, &kk, &a[a_offset], lda, &d__[1], &e[1], &tau[1], &iinfo);
    } else {

        /*        Reduce the lower triangle of A */

        i__2 = *n - nx;
        i__1 = nb;
        for (i__ = 1; i__1 < 0 ? i__ >= i__2 : i__ <= i__2; i__ += i__1) {

            /*           Reduce columns i:i+nb-1 to tridiagonal form and form the */
            /*           matrix W which is needed to update the unreduced part of */
            /*           the matrix */

            i__3 = *n - i__ + 1;
            slatrd_(uplo, &i__3, &nb, &a[i__ + i__ * a_dim1], lda, &e[i__], &
                    tau[i__], &work[1], &ldwork);

            /*           Update the unreduced submatrix A(i+ib:n,i+ib:n), using */
            /*           an update of the form:  A := A - V*W' - W*V' */

            i__3 = *n - i__ - nb + 1;
            ssyr2k_(uplo, "No transpose", &i__3, &nb, &c_b22, &a[i__ + nb +
                    i__ * a_dim1], lda, &work[nb + 1], &ldwork, &c_b23, &a[
                        i__ + nb + (i__ + nb) * a_dim1], lda);

            /*           Copy subdiagonal elements back into A, and diagonal */
            /*           elements into D */

            i__3 = i__ + nb - 1;
            for (j = i__; j <= i__3; ++j) {
                a[j + 1 + j * a_dim1] = e[j];
                d__[j] = a[j + j * a_dim1];
                /* L30: */
            }
            /* L40: */
        }

        /*        Use unblocked code to reduce the last or only block */

        i__1 = *n - i__ + 1;
        ssytd2_(uplo, &i__1, &a[i__ + i__ * a_dim1], lda, &d__[i__], &e[i__],
                &tau[i__], &iinfo);
    }

    work[1] = (real) lwkopt;
    return 0;

    /*     End of SSYTRD */

} /* ssytrd_ */
Exemplo n.º 2
0
/* Subroutine */ int ssytrd_(char *uplo, integer *n, real *a, integer *lda, 
	real *d, real *e, real *tau, real *work, integer *lwork, integer *
	info)
{
/*  -- LAPACK routine (version 2.0) --   
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
       Courant Institute, Argonne National Lab, and Rice University   
       September 30, 1994   


    Purpose   
    =======   

    SSYTRD reduces a real symmetric matrix A to real symmetric   
    tridiagonal form T by an orthogonal similarity transformation:   
    Q**T * A * Q = T.   

    Arguments   
    =========   

    UPLO    (input) CHARACTER*1   
            = 'U':  Upper triangle of A is stored;   
            = 'L':  Lower triangle of A is stored.   

    N       (input) INTEGER   
            The order of the matrix A.  N >= 0.   

    A       (input/output) REAL array, dimension (LDA,N)   
            On entry, the symmetric matrix A.  If UPLO = 'U', the leading 
  
            N-by-N upper triangular part of A contains the upper   
            triangular part of the matrix A, and the strictly lower   
            triangular part of A is not referenced.  If UPLO = 'L', the   
            leading N-by-N lower triangular part of A contains the lower 
  
            triangular part of the matrix A, and the strictly upper   
            triangular part of A is not referenced.   
            On exit, if UPLO = 'U', the diagonal and first superdiagonal 
  
            of A are overwritten by the corresponding elements of the   
            tridiagonal matrix T, and the elements above the first   
            superdiagonal, with the array TAU, represent the orthogonal   
            matrix Q as a product of elementary reflectors; if UPLO   
            = 'L', the diagonal and first subdiagonal of A are over-   
            written by the corresponding elements of the tridiagonal   
            matrix T, and the elements below the first subdiagonal, with 
  
            the array TAU, represent the orthogonal matrix Q as a product 
  
            of elementary reflectors. See Further Details.   

    LDA     (input) INTEGER   
            The leading dimension of the array A.  LDA >= max(1,N).   

    D       (output) REAL array, dimension (N)   
            The diagonal elements of the tridiagonal matrix T:   
            D(i) = A(i,i).   

    E       (output) REAL array, dimension (N-1)   
            The off-diagonal elements of the tridiagonal matrix T:   
            E(i) = A(i,i+1) if UPLO = 'U', E(i) = A(i+1,i) if UPLO = 'L'. 
  

    TAU     (output) REAL array, dimension (N-1)   
            The scalar factors of the elementary reflectors (see Further 
  
            Details).   

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

    LWORK   (input) INTEGER   
            The dimension of the array WORK.  LWORK >= 1.   
            For optimum performance LWORK >= N*NB, where NB is the   
            optimal blocksize.   

    INFO    (output) INTEGER   
            = 0:  successful exit   
            < 0:  if INFO = -i, the i-th argument had an illegal value   

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

    If UPLO = 'U', the matrix Q is represented as a product of elementary 
  
    reflectors   

       Q = H(n-1) . . . H(2) H(1).   

    Each H(i) has the form   

       H(i) = I - tau * v * v'   

    where tau is a real scalar, and v is a real vector with   
    v(i+1:n) = 0 and v(i) = 1; v(1:i-1) is stored on exit in   
    A(1:i-1,i+1), and tau in TAU(i).   

    If UPLO = 'L', the matrix Q is represented as a product of elementary 
  
    reflectors   

       Q = H(1) H(2) . . . H(n-1).   

    Each H(i) has the form   

       H(i) = I - tau * v * v'   

    where tau is a real scalar, and v is a real vector with   
    v(1:i) = 0 and v(i+1) = 1; v(i+2:n) is stored on exit in A(i+2:n,i), 
  
    and tau in TAU(i).   

    The contents of A on exit are illustrated by the following examples   
    with n = 5:   

    if UPLO = 'U':                       if UPLO = 'L':   

      (  d   e   v2  v3  v4 )              (  d                  )   
      (      d   e   v3  v4 )              (  e   d              )   
      (          d   e   v4 )              (  v1  e   d          )   
      (              d   e  )              (  v1  v2  e   d      )   
      (                  d  )              (  v1  v2  v3  e   d  )   

    where d and e denote diagonal and off-diagonal elements of T, and vi 
  
    denotes an element of the vector defining H(i).   

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


       Test the input parameters   

    
   Parameter adjustments   
       Function Body */
    /* Table of constant values */
    static integer c__1 = 1;
    static integer c_n1 = -1;
    static integer c__3 = 3;
    static integer c__2 = 2;
    static real c_b22 = -1.f;
    static real c_b23 = 1.f;
    
    /* System generated locals */
    integer a_dim1, a_offset, i__1, i__2, i__3;
    /* Local variables */
    static integer i, j;
    extern logical lsame_(char *, char *);
    static integer nbmin, iinfo;
    static logical upper;
    static integer nb, kk;
    extern /* Subroutine */ int ssytd2_(char *, integer *, real *, integer *, 
	    real *, real *, real *, integer *), ssyr2k_(char *, char *
	    , integer *, integer *, real *, real *, integer *, real *, 
	    integer *, real *, real *, integer *);
    static integer nx;
    extern /* Subroutine */ int xerbla_(char *, integer *);
    extern integer ilaenv_(integer *, char *, char *, integer *, integer *, 
	    integer *, integer *, ftnlen, ftnlen);
    extern /* Subroutine */ int slatrd_(char *, integer *, integer *, real *, 
	    integer *, real *, real *, real *, integer *);
    static integer ldwork, iws;



#define D(I) d[(I)-1]
#define E(I) e[(I)-1]
#define TAU(I) tau[(I)-1]
#define WORK(I) work[(I)-1]

#define A(I,J) a[(I)-1 + ((J)-1)* ( *lda)]

    *info = 0;
    upper = lsame_(uplo, "U");
    if (! upper && ! lsame_(uplo, "L")) {
	*info = -1;
    } else if (*n < 0) {
	*info = -2;
    } else if (*lda < max(1,*n)) {
	*info = -4;
    } else if (*lwork < 1) {
	*info = -9;
    }
    if (*info != 0) {
	i__1 = -(*info);
	xerbla_("SSYTRD", &i__1);
	return 0;
    }

/*     Quick return if possible */

    if (*n == 0) {
	WORK(1) = 1.f;
	return 0;
    }

/*     Determine the block size. */

    nb = ilaenv_(&c__1, "SSYTRD", uplo, n, &c_n1, &c_n1, &c_n1, 6L, 1L);
    nx = *n;
    iws = 1;
    if (nb > 1 && nb < *n) {

/*        Determine when to cross over from blocked to unblocked code 
  
          (last block is always handled by unblocked code).   

   Computing MAX */
	i__1 = nb, i__2 = ilaenv_(&c__3, "SSYTRD", uplo, n, &c_n1, &c_n1, &
		c_n1, 6L, 1L);
	nx = max(i__1,i__2);
	if (nx < *n) {

/*           Determine if workspace is large enough for blocked co
de. */

	    ldwork = *n;
	    iws = ldwork * nb;
	    if (*lwork < iws) {

/*              Not enough workspace to use optimal NB:  deter
mine the   
                minimum value of NB, and reduce NB or force us
e of   
                unblocked code by setting NX = N.   

   Computing MAX */
		i__1 = *lwork / ldwork;
		nb = max(i__1,1);
		nbmin = ilaenv_(&c__2, "SSYTRD", uplo, n, &c_n1, &c_n1, &c_n1,
			 6L, 1L);
		if (nb < nbmin) {
		    nx = *n;
		}
	    }
	} else {
	    nx = *n;
	}
    } else {
	nb = 1;
    }

    if (upper) {

/*        Reduce the upper triangle of A.   
          Columns 1:kk are handled by the unblocked method. */

	kk = *n - (*n - nx + nb - 1) / nb * nb;
	i__1 = kk + 1;
	i__2 = -nb;
	for (i = *n - nb + 1; -nb < 0 ? i >= kk+1 : i <= kk+1; i += -nb) {

/*           Reduce columns i:i+nb-1 to tridiagonal form and form 
the   
             matrix W which is needed to update the unreduced part
 of   
             the matrix */

	    i__3 = i + nb - 1;
	    slatrd_(uplo, &i__3, &nb, &A(1,1), lda, &E(1), &TAU(1), &
		    WORK(1), &ldwork);

/*           Update the unreduced submatrix A(1:i-1,1:i-1), using 
an   
             update of the form:  A := A - V*W' - W*V' */

	    i__3 = i - 1;
	    ssyr2k_(uplo, "No transpose", &i__3, &nb, &c_b22, &A(1,i), lda, &WORK(1), &ldwork, &c_b23, &A(1,1), lda);

/*           Copy superdiagonal elements back into A, and diagonal
   
             elements into D */

	    i__3 = i + nb - 1;
	    for (j = i; j <= i+nb-1; ++j) {
		A(j-1,j) = E(j - 1);
		D(j) = A(j,j);
/* L10: */
	    }
/* L20: */
	}

/*        Use unblocked code to reduce the last or only block */

	ssytd2_(uplo, &kk, &A(1,1), lda, &D(1), &E(1), &TAU(1), &iinfo);
    } else {

/*        Reduce the lower triangle of A */

	i__2 = *n - nx;
	i__1 = nb;
	for (i = 1; nb < 0 ? i >= *n-nx : i <= *n-nx; i += nb) {

/*           Reduce columns i:i+nb-1 to tridiagonal form and form 
the   
             matrix W which is needed to update the unreduced part
 of   
             the matrix */

	    i__3 = *n - i + 1;
	    slatrd_(uplo, &i__3, &nb, &A(i,i), lda, &E(i), &TAU(i),
		     &WORK(1), &ldwork);

/*           Update the unreduced submatrix A(i+ib:n,i+ib:n), usin
g   
             an update of the form:  A := A - V*W' - W*V' */

	    i__3 = *n - i - nb + 1;
	    ssyr2k_(uplo, "No transpose", &i__3, &nb, &c_b22, &A(i+nb,i), lda, &WORK(nb + 1), &ldwork, &c_b23, &A(i+nb,i+nb), lda);

/*           Copy subdiagonal elements back into A, and diagonal 
  
             elements into D */

	    i__3 = i + nb - 1;
	    for (j = i; j <= i+nb-1; ++j) {
		A(j+1,j) = E(j);
		D(j) = A(j,j);
/* L30: */
	    }
/* L40: */
	}

/*        Use unblocked code to reduce the last or only block */

	i__1 = *n - i + 1;
	ssytd2_(uplo, &i__1, &A(i,i), lda, &D(i), &E(i), &TAU(i), &
		iinfo);
    }

    WORK(1) = (real) iws;
    return 0;

/*     End of SSYTRD */

} /* ssytrd_ */