LAPACK  3.4.2
LAPACK: Linear Algebra PACKage
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dorgtr.f File Reference

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Functions/Subroutines

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

Function/Subroutine Documentation

subroutine dorgtr ( character  UPLO,
integer  N,
double precision, dimension( lda, * )  A,
integer  LDA,
double precision, dimension( * )  TAU,
double precision, dimension( * )  WORK,
integer  LWORK,
integer  INFO 
)

DORGTR

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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:
[in]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.
[in]N
          N is INTEGER
          The order of the matrix Q. N >= 0.
[in,out]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.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A. LDA >= max(1,N).
[in]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.
[out]WORK
          WORK is DOUBLE PRECISION 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-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.
[out]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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