dorghr.f man page

subroutine dorghr (N, ILO, IHI, A, LDA, TAU, WORK, LWORK, INFO)
DORGHR

DORGHR  

Purpose:

 DORGHR generates a real orthogonal matrix Q which is defined as the
 product of IHI-ILO elementary reflectors of order N, as returned by
 DGEHRD:

 Q = H(ilo) H(ilo+1) . . . H(ihi-1).

Parameters:

N

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

ILO

          ILO is INTEGER

IHI

          IHI is INTEGER

          ILO and IHI must have the same values as in the previous call
          of DGEHRD. Q is equal to the unit matrix except in the
          submatrix Q(ilo+1:ihi,ilo+1:ihi).
          1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.

A

          A is DOUBLE PRECISION array, dimension (LDA,N)
          On entry, the vectors which define the elementary reflectors,
          as returned by DGEHRD.
          On exit, the N-by-N orthogonal matrix Q.

LDA

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

TAU

          TAU is DOUBLE PRECISION array, dimension (N-1)
          TAU(i) must contain the scalar factor of the elementary
          reflector H(i), as returned by DGEHRD.

WORK

          WORK is DOUBLE PRECISION 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 >= IHI-ILO.
          For optimum performance LWORK >= (IHI-ILO)*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.

Date:

December 2016

Definition at line 128 of file dorghr.f.