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

NAME

zungtr - generate a complex unitary matrix Q which is defined as the product of n-1 elementary reflectors of order N, as returned by CHETRD

SYNOPSIS

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

  SUBROUTINE ZUNGTR_64( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO)
  CHARACTER * 1 UPLO
  DOUBLE COMPLEX A(LDA,*), TAU(*), WORK(*)
  INTEGER*8 N, LDA, LWORK, INFO

F95 INTERFACE

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

  SUBROUTINE UNGTR_64( UPLO, [N], A, [LDA], TAU, [WORK], [LWORK], 
 *       [INFO])
  CHARACTER(LEN=1) :: UPLO
  COMPLEX(8), DIMENSION(:) :: TAU, WORK
  COMPLEX(8), DIMENSION(:,:) :: A
  INTEGER(8) :: N, LDA, LWORK, INFO

C INTERFACE

#include <sunperf.h>

void zungtr(char uplo, int n, doublecomplex *a, int lda, doublecomplex *tau, int *info);

void zungtr_64(char uplo, long n, doublecomplex *a, long lda, doublecomplex *tau, long *info);

PURPOSE

zungtr generates a complex unitary matrix Q which is defined as the product of n-1 elementary reflectors of order N, as returned by CHETRD:

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 CHETRD;
   = 'L': Lower triangle of A contains elementary reflectors
  from CHETRD.

• 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 CHETRD. On exit, the N-by-N unitary matrix Q.

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

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

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

• LWORK (input)
  The dimension of the array WORK. LWORK > = 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