table of contents
/home/abuild/rpmbuild/BUILD/lapack-3.12.0/SRC/cungbr.f(3) | Library Functions Manual | /home/abuild/rpmbuild/BUILD/lapack-3.12.0/SRC/cungbr.f(3) |
NAME¶
/home/abuild/rpmbuild/BUILD/lapack-3.12.0/SRC/cungbr.f
SYNOPSIS¶
Functions/Subroutines¶
subroutine CUNGBR (vect, m, n, k, a, lda, tau, work, lwork,
info)
CUNGBR
Function/Subroutine Documentation¶
subroutine CUNGBR (character vect, integer m, integer n, integer k, complex, dimension( lda, * ) a, integer lda, complex, dimension( * ) tau, complex, dimension( * ) work, integer lwork, integer info)¶
CUNGBR
Purpose:
!> !> CUNGBR generates one of the complex unitary matrices Q or P**H !> determined by CGEBRD when reducing a complex matrix A to bidiagonal !> form: A = Q * B * P**H. Q and P**H are defined as products of !> elementary reflectors H(i) or G(i) respectively. !> !> If VECT = 'Q', A is assumed to have been an M-by-K matrix, and Q !> is of order M: !> if m >= k, Q = H(1) H(2) . . . H(k) and CUNGBR returns the first n !> columns of Q, where m >= n >= k; !> if m < k, Q = H(1) H(2) . . . H(m-1) and CUNGBR returns Q as an !> M-by-M matrix. !> !> If VECT = 'P', A is assumed to have been a K-by-N matrix, and P**H !> is of order N: !> if k < n, P**H = G(k) . . . G(2) G(1) and CUNGBR returns the first m !> rows of P**H, where n >= m >= k; !> if k >= n, P**H = G(n-1) . . . G(2) G(1) and CUNGBR returns P**H as !> an N-by-N matrix. !>
Parameters
VECT
!> VECT is CHARACTER*1 !> Specifies whether the matrix Q or the matrix P**H is !> required, as defined in the transformation applied by CGEBRD: !> = 'Q': generate Q; !> = 'P': generate P**H. !>
M
!> M is INTEGER !> The number of rows of the matrix Q or P**H to be returned. !> M >= 0. !>
N
!> N is INTEGER !> The number of columns of the matrix Q or P**H to be returned. !> N >= 0. !> If VECT = 'Q', M >= N >= min(M,K); !> if VECT = 'P', N >= M >= min(N,K). !>
K
!> K is INTEGER !> If VECT = 'Q', the number of columns in the original M-by-K !> matrix reduced by CGEBRD. !> If VECT = 'P', the number of rows in the original K-by-N !> matrix reduced by CGEBRD. !> K >= 0. !>
A
!> A is COMPLEX array, dimension (LDA,N) !> On entry, the vectors which define the elementary reflectors, !> as returned by CGEBRD. !> On exit, the M-by-N matrix Q or P**H. !>
LDA
!> LDA is INTEGER !> The leading dimension of the array A. LDA >= M. !>
TAU
!> TAU is COMPLEX array, dimension !> (min(M,K)) if VECT = 'Q' !> (min(N,K)) if VECT = 'P' !> TAU(i) must contain the scalar factor of the elementary !> reflector H(i) or G(i), which determines Q or P**H, as !> returned by CGEBRD in its array argument TAUQ or TAUP. !>
WORK
!> WORK is COMPLEX 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,min(M,N)). !> For optimum performance LWORK >= min(M,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
!> 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.
Definition at line 156 of file cungbr.f.
Author¶
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