LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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◆ sorgql()

subroutine sorgql ( integer m,
integer n,
integer k,
real, dimension( lda, * ) a,
integer lda,
real, dimension( * ) tau,
real, dimension( * ) work,
integer lwork,
integer info )

SORGQL

Download SORGQL + dependencies [TGZ] [ZIP] [TXT]

Purpose:
!>
!> SORGQL generates an M-by-N real matrix Q with orthonormal columns,
!> which is defined as the last N columns of a product of K elementary
!> reflectors of order M
!>
!>       Q  =  H(k) . . . H(2) H(1)
!>
!> as returned by SGEQLF.
!>
Parameters
[in]M
!>          M is INTEGER
!>          The number of rows of the matrix Q. M >= 0.
!>
[in]N
!>          N is INTEGER
!>          The number of columns of the matrix Q. M >= N >= 0.
!>
[in]K
!>          K is INTEGER
!>          The number of elementary reflectors whose product defines the
!>          matrix Q. N >= K >= 0.
!>
[in,out]A
!>          A is REAL array, dimension (LDA,N)
!>          On entry, the (n-k+i)-th column must contain the vector which
!>          defines the elementary reflector H(i), for i = 1,2,...,k, as
!>          returned by SGEQLF in the last k columns of its array
!>          argument A.
!>          On exit, the M-by-N matrix Q.
!>
[in]LDA
!>          LDA is INTEGER
!>          The first dimension of the array A. LDA >= max(1,M).
!>
[in]TAU
!>          TAU is REAL array, dimension (K)
!>          TAU(i) must contain the scalar factor of the elementary
!>          reflector H(i), as returned by SGEQLF.
!>
[out]WORK
!>          WORK is REAL array, dimension (MAX(1,LWORK))
!>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
!>
[in]LWORK
!>          LWORK is INTEGER
!>          The dimension of the array WORK. LWORK >= max(1,N).
!>          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.
!>
[out]INFO
!>          INFO is INTEGER
!>          = 0:  successful exit
!>          < 0:  if INFO = -i, the i-th argument has an illegal value
!>
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.