zungtr.f - Man Page

subroutine zungtr (uplo, n, a, lda, tau, work, lwork, info)
ZUNGTR

ZUNGTR  

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
 ZHETRD:

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

N

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

A

          A is COMPLEX*16 array, dimension (LDA,N)
          On entry, the vectors which define the elementary reflectors,
          as returned by ZHETRD.
          On exit, the N-by-N unitary matrix Q.

LDA

          LDA is INTEGER
          The leading dimension of the array A. LDA >= N.

TAU

          TAU is COMPLEX*16 array, dimension (N-1)
          TAU(i) must contain the scalar factor of the elementary
          reflector H(i), as returned by ZHETRD.

WORK

          WORK is COMPLEX*16 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 >= 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.

Definition at line 122 of file zungtr.f.