• NAME
• SYNOPSIS
• F95 INTERFACE
• C INTERFACE
• PURPOSE
• ARGUMENTS

NAME

dorgtr - generate a real orthogonal matrix Q which is defined as the product of n-1 elementary reflectors of order N, as returned by SSYTRD

SYNOPSIS

  SUBROUTINE DORGTR( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO)
  CHARACTER * 1 UPLO
  INTEGER N, LDA, LWORK, INFO
  DOUBLE PRECISION A(LDA,*), TAU(*), WORK(*)

  SUBROUTINE DORGTR_64( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO)
  CHARACTER * 1 UPLO
  INTEGER*8 N, LDA, LWORK, INFO
  DOUBLE PRECISION A(LDA,*), TAU(*), WORK(*)

F95 INTERFACE

  SUBROUTINE ORGTR( UPLO, [N], A, [LDA], TAU, [WORK], [LWORK], [INFO])
  CHARACTER(LEN=1) :: UPLO
  INTEGER :: N, LDA, LWORK, INFO
  REAL(8), DIMENSION(:) :: TAU, WORK
  REAL(8), DIMENSION(:,:) :: A

  SUBROUTINE ORGTR_64( UPLO, [N], A, [LDA], TAU, [WORK], [LWORK], 
 *       [INFO])
  CHARACTER(LEN=1) :: UPLO
  INTEGER(8) :: N, LDA, LWORK, INFO
  REAL(8), DIMENSION(:) :: TAU, WORK
  REAL(8), DIMENSION(:,:) :: A

C INTERFACE

#include <sunperf.h>

void dorgtr(char uplo, int n, double *a, int lda, double *tau, int *info);

void dorgtr_64(char uplo, long n, double *a, long lda, double *tau, long *info);

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 SSYTRD:

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

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

ARGUMENTS

• UPLO (input)
  

   = 'U': Upper triangle of A contains elementary reflectors
  from SSYTRD;
   = 'L': Lower triangle of A contains elementary reflectors
  from SSYTRD.

• N (input)
  The order of the matrix Q. N > = 0.

• A (input/output)
  On entry, the vectors which define the elementary reflectors, as returned by SSYTRD. On exit, the N-by-N orthogonal matrix Q.

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

• TAU (input)
  TAU(i) must contain the scalar factor of the elementary reflector H(i), as returned by SSYTRD.

• WORK (workspace)
  On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

• LWORK (input)
  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 (output)
  

   = 0:  successful exit

   < 0:  if INFO  = -i, the i-th argument had an illegal value