NAME

       sorghr.f -

SYNOPSIS

   Functions/Subroutines
       subroutine sorghr (N, ILO, IHI, A, LDA, TAU, WORK, LWORK, INFO)
           SORGHR

Function/Subroutine Documentation

   subroutine sorghr (integer N, integer ILO, integer IHI, real, dimension( lda, * ) A, integer
       LDA, real, dimension( * ) TAU, real, dimension( * ) WORK, integer LWORK, integer INFO)
       SORGHR

       Purpose:

            SORGHR generates a real orthogonal matrix Q which is defined as the
            product of IHI-ILO elementary reflectors of order N, as returned by
            SGEHRD:

            Q = H(ilo) H(ilo+1) . . . H(ihi-1).

       Parameters:
           N

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

           ILO

                     ILO is INTEGER

           IHI

                     IHI is INTEGER

                     ILO and IHI must have the same values as in the previous call
                     of SGEHRD. Q is equal to the unit matrix except in the
                     submatrix Q(ilo+1:ihi,ilo+1:ihi).
                     1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.

           A

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

           LDA

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

           TAU

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

           WORK

                     WORK is REAL 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 >= IHI-ILO.
                     For optimum performance LWORK >= (IHI-ILO)*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.

       Date:
           November 2011

Author

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