SRC/ztzrzf.f(3)

NAME
SRC/ztzrzf.f

SYNOPSIS

  Functions/Subroutines
subroutine ztzrzf (m, n, a, lda, tau, work, lwork, info)
ZTZRZF

Function/Subroutine Documentation

  subroutine ztzrzf (integer m, integer n, complex*16, dimension( lda, * ) a, integer lda, complex*16, dimension( * ) tau, complex*16, dimension( * ) work, integer lwork, integer info)

ZTZRZF

Purpose:

     ZTZRZF reduces the M-by-N ( M<=N ) complex upper trapezoidal matrix A
     to upper triangular form by means of unitary transformations.
     The upper trapezoidal matrix A is factored as
        A = ( R  0 ) * Z,
     where Z is an N-by-N unitary matrix and R is an M-by-M upper
     triangular matrix.

Parameters
    M

              M is INTEGER
              The number of rows of the matrix A.  M >= 0.

    N

              N is INTEGER
              The number of columns of the matrix A.  N >= M.

    A

              A is COMPLEX*16 array, dimension (LDA,N)
              On entry, the leading M-by-N upper trapezoidal part of the
              array A must contain the matrix to be factorized.
              On exit, the leading M-by-M upper triangular part of A
              contains the upper triangular matrix R, and elements M+1 to
              N of the first M rows of A, with the array TAU, represent the
              unitary matrix Z as a product of M elementary reflectors.

    LDA

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

    TAU

              TAU is COMPLEX*16 array, dimension (M)
              The scalar factors of the elementary reflectors.

    WORK

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

    LWORK

              LWORK is INTEGER
              The dimension of the array WORK.  LWORK >= max(1,M).
              For optimum performance LWORK >= M*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

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

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Contributors:
    A. Petitet, Computer Science Dept., Univ. of Tenn., Knoxville, USA

Further Details:

      The N-by-N matrix Z can be computed by
         Z =  Z(1)*Z(2)* ... *Z(M)
      where each N-by-N Z(k) is given by
         Z(k) = I - tau(k)*v(k)*v(k)**H
      with v(k) is the kth row vector of the M-by-N matrix
         V = ( I   A(:,M+1:N) )
      I is the M-by-M identity matrix, A(:,M+1:N)
      is the output stored in A on exit from ZTZRZF,
      and tau(k) is the kth element of the array TAU.

Definition at line 150 of file ztzrzf.f.

Author

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