SORGR2 generates an m by n real matrix Q with orthonormal rows,
 which is defined as the last m rows of a product of k elementary
 reflectors of order n

       Q  =  H(1) H(2) . . . H(k)

 as returned by SGERQF.

          M is INTEGER
          The number of rows of the matrix Q. M >= 0.

          N is INTEGER
          The number of columns of the matrix Q. N >= M.

          K is INTEGER
          The number of elementary reflectors whose product defines the
          matrix Q. M >= K >= 0.

          A is REAL array, dimension (LDA,N)
          On entry, the (m-k+i)-th row must contain the vector which
          defines the elementary reflector H(i), for i = 1,2,...,k, as
          returned by SGERQF in the last k rows of its array argument
          A.
          On exit, the m by n matrix Q.

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

          TAU is REAL array, dimension (K)
          TAU(i) must contain the scalar factor of the elementary
          reflector H(i), as returned by SGERQF.

          WORK is REAL array, dimension (M)

          INFO is INTEGER
          = 0: successful exit
          < 0: if INFO = -i, the i-th argument has an illegal value