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        ZGERQ2 - compute an RQ factorization of a complex m by n matrix A


            INTEGER        INFO, LDA, M, N
            COMPLEX*16     A( LDA, * ), TAU( * ), WORK( * )


        ZGERQ2 computes an RQ factorization of a complex m by n matrix A: A = R
        * Q.


        M       (input) INTEGER
                The number of rows of the matrix A.  M >= 0.
        N       (input) INTEGER
                The number of columns of the matrix A.  N >= 0.
        A       (input/output) COMPLEX*16 array, dimension (LDA,N)
                On entry, the m by n matrix A.  On exit, if m <= n,  the  upper
                triangle  of  the  subarray  A(1:m,n-m+1:n) contains the m by m
                upper triangular matrix R; if m >= n, the elements on and above
                the  (m-n)-th  subdiagonal contain the m by n upper trapezoidal
                matrix R; the remaining elements, with the array TAU, represent
                the unitary matrix Q as a product of elementary reflectors (see
                Further Details).
        LDA     (input) INTEGER
                The leading dimension of the array A.  LDA >= max(1,M).
        TAU     (output) COMPLEX*16 array, dimension (min(M,N))
                The scalar factors of the elementary  reflectors  (see  Further
        WORK    (workspace) COMPLEX*16 array, dimension (M)
        INFO    (output) INTEGER
                = 0: successful exit
                < 0: if INFO = -i, the i-th argument had an illegal value
        The matrix Q is represented as a product of elementary reflectors
H(2)ā€™ . . . H(k)ā€™, where k = min(m,n).
        Each H(i) has the form
           H(i) = I - tau * v * vā€™
        where  tau  is  a  complex  scalar, and v is a complex vector with v(n-
        k+i+1:n) = 0 and v(n-k+i) = 1; conjg(v(1:n-k+i-1)) is stored on exit in
        A(m-k+i,1:n-k+i-1), and tau in TAU(i).


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