dorgtr (3)

Functions/Subroutines

subroutine dorgtr (UPLO, N, A, LDA, TAU, WORK, LWORK, INFO)

DORGTR

subroutine dorgtr (characterUPLO, integerN, double precision, dimension( lda, * )A, integerLDA, double precision, dimension( * )TAU, double precision, dimension( * )WORK, integerLWORK, integerINFO)

DORGTR

Purpose:

 DORGTR generates a real orthogonal matrix Q which is defined as the
 product of n-1 elementary reflectors of order N, as returned by
 DSYTRD:

 if UPLO = 'U', Q = H(n-1) . . . H(2) H(1),

 if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).

Parameters:

UPLO

          UPLO is CHARACTER*1
          = 'U': Upper triangle of A contains elementary reflectors
                 from DSYTRD;
          = 'L': Lower triangle of A contains elementary reflectors
                 from DSYTRD.

N

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

A

          A is DOUBLE PRECISION array, dimension (LDA,N)
          On entry, the vectors which define the elementary reflectors,
          as returned by DSYTRD.
          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 DSYTRD.

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 >= max(1,N-1).
          For optimum performance LWORK >= (N-1)*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:

November 2011

Definition at line 124 of file dorgtr.f.

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