SRC/zgemqr.f(3) Library Functions Manual SRC/zgemqr.f(3)

SRC/zgemqr.f


subroutine zgemqr (side, trans, m, n, k, a, lda, t, tsize, c, ldc, work, lwork, info)
ZGEMQR

ZGEMQR

Purpose:

!>
!> ZGEMQR overwrites the general real M-by-N matrix C with
!>
!>                      SIDE = 'L'     SIDE = 'R'
!>      TRANS = 'N':      Q * C          C * Q
!>      TRANS = 'T':      Q**H * C       C * Q**H
!>
!> where Q is a complex unitary matrix defined as the product
!> of blocked elementary reflectors computed by tall skinny
!> QR factorization (ZGEQR)
!>
!> 

Parameters

SIDE
!>          SIDE is CHARACTER*1
!>          = 'L': apply Q or Q**H from the Left;
!>          = 'R': apply Q or Q**H from the Right.
!> 

TRANS

!>          TRANS is CHARACTER*1
!>          = 'N':  No transpose, apply Q;
!>          = 'C':  Conjugate transpose, apply Q**H.
!> 

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 C. N >= 0.
!> 

K

!>          K is INTEGER
!>          The number of elementary reflectors whose product defines
!>          the matrix Q.
!>          If SIDE = 'L', M >= K >= 0;
!>          if SIDE = 'R', N >= K >= 0.
!> 

A

!>          A is COMPLEX*16 array, dimension (LDA,K)
!>          Part of the data structure to represent Q as returned by ZGEQR.
!> 

LDA

!>          LDA is INTEGER
!>          The leading dimension of the array A.
!>          If SIDE = 'L', LDA >= max(1,M);
!>          if SIDE = 'R', LDA >= max(1,N).
!> 

T

!>          T is COMPLEX*16 array, dimension (MAX(5,TSIZE)).
!>          Part of the data structure to represent Q as returned by ZGEQR.
!> 

TSIZE

!>          TSIZE is INTEGER
!>          The dimension of the array T. TSIZE >= 5.
!> 

C

!>          C is COMPLEX*16 array, dimension (LDC,N)
!>          On entry, the M-by-N matrix C.
!>          On exit, C is overwritten by Q*C or Q**H*C or C*Q**H or C*Q.
!> 

LDC

!>          LDC is INTEGER
!>          The leading dimension of the array C. LDC >= max(1,M).
!> 

WORK

!>          (workspace) COMPLEX*16 array, dimension (MAX(1,LWORK))
!>          On exit, if INFO = 0, WORK(1) returns the minimal LWORK.
!> 

LWORK

!>          LWORK is INTEGER
!>          The dimension of the array WORK. LWORK >= 1.
!>          If LWORK = -1, then a workspace query is assumed. The routine
!>          only calculates the size of the WORK array, returns this
!>          value as WORK(1), and no error message related to WORK
!>          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.

Further Details

!>
!> These details are particular for this LAPACK implementation. Users should not
!> take them for granted. These details may change in the future, and are not likely
!> true for another LAPACK implementation. These details are relevant if one wants
!> to try to understand the code. They are not part of the interface.
!>
!> In this version,
!>
!>          T(2): row block size (MB)
!>          T(3): column block size (NB)
!>          T(6:TSIZE): data structure needed for Q, computed by
!>                           ZLATSQR or ZGEQRT
!>
!>  Depending on the matrix dimensions M and N, and row and column
!>  block sizes MB and NB returned by ILAENV, ZGEQR will use either
!>  ZLATSQR (if the matrix is tall-and-skinny) or ZGEQRT to compute
!>  the QR factorization.
!>  This version of ZGEMQR will use either ZLAMTSQR or ZGEMQRT to
!>  multiply matrix Q by another matrix.
!>  Further Details in ZLAMTSQR or ZGEMQRT.
!>
!> 

Definition at line 173 of file zgemqr.f.

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