SRC/zsyequb.f(3)

NAME
SRC/zsyequb.f

SYNOPSIS

  Functions/Subroutines
subroutine zsyequb (uplo, n, a, lda, s, scond, amax, work, info)
ZSYEQUB

Function/Subroutine Documentation

  subroutine zsyequb (character uplo, integer n, complex*16, dimension( lda, * ) a, integer lda, double precision, dimension( * ) s, double precision scond, double precision amax, complex*16, dimension( * ) work, integer info)

ZSYEQUB

Purpose:

    !>
    !> ZSYEQUB computes row and column scalings intended to equilibrate a
    !> symmetric matrix A (with respect to the Euclidean norm) and reduce
    !> its condition number. The scale factors S are computed by the BIN
    !> algorithm (see references) so that the scaled matrix B with elements
    !> B(i,j) = S(i)*A(i,j)*S(j) has a condition number within a factor N of
    !> the smallest possible condition number over all possible diagonal
    !> scalings.
    !>

Parameters
    UPLO

    !>          UPLO is CHARACTER*1
    !>          = 'U':  Upper triangle of A is stored;
    !>          = 'L':  Lower triangle of A is stored.
    !>

    N

    !>          N is INTEGER
    !>          The order of the matrix A. N >= 0.
    !>

    A

    !>          A is COMPLEX*16 array, dimension (LDA,N)
    !>          The N-by-N symmetric matrix whose scaling factors are to be
    !>          computed.
    !>

    LDA

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

    S

    !>          S is DOUBLE PRECISION array, dimension (N)
    !>          If INFO = 0, S contains the scale factors for A.
    !>

    SCOND

    !>          SCOND is DOUBLE PRECISION
    !>          If INFO = 0, S contains the ratio of the smallest S(i) to
    !>          the largest S(i). If SCOND >= 0.1 and AMAX is neither too
    !>          large nor too small, it is not worth scaling by S.
    !>

    AMAX

    !>          AMAX is DOUBLE PRECISION
    !>          Largest absolute value of any matrix element. If AMAX is
    !>          very close to overflow or very close to underflow, the
    !>          matrix should be scaled.
    !>

    WORK

    !>          WORK is COMPLEX*16 array, dimension (2*N)
    !>

    INFO

    !>          INFO is INTEGER
    !>          = 0:  successful exit
    !>          < 0:  if INFO = -i, the i-th argument had an illegal value
    !>          > 0:  if INFO = i, the i-th diagonal element is nonpositive.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

References:
    Livne, O.E. and Golub, G.H., 'Scaling by Binormalization',
    Numerical Algorithms, vol. 35, no. 1, pp. 97-120, January 2004.
    DOI 10.1023/B:NUMA.0000016606.32820.69
    Tech report version: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.3.1679

Definition at line 131 of file zsyequb.f.

Author

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