CUNGTR(3)      LAPACK routine of NEC Numeric Library Collection      CUNGTR(3)



NAME
       CUNGTR

SYNOPSIS
       SUBROUTINE CUNGTR (UPLO, N, A, LDA, TAU, WORK, LWORK, INFO)



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

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

           A         (input/output)
                     A is COMPLEX array, dimension (LDA,N)
                     On entry, the vectors which define the elementary reflectors,
                     as returned by CHETRD.
                     On exit, the N-by-N unitary matrix Q.

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

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

           WORK      (output)
                     WORK is COMPLEX array, dimension (MAX(1,LWORK))
                     On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

           LWORK     (input)
                     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      (output)
                     INFO is INTEGER
                     = 0:  successful exit
                     < 0:  if INFO = -i, the i-th argument had an illegal value



LAPACK routine                  31 October 2017                      CUNGTR(3)