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



NAME
       SORGTR

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



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

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

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

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

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

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



LAPACK routine                  31 October 2017                      SORGTR(3)