H(i).

    This implementation follows the hybrid algorithm and notations described in

    S. Tomov and J. Dongarra, "Accelerating the reduction to upper Hessenberg
    form through hybrid GPU-based computing," University of Tennessee Computer
    Science Technical Report, UT-CS-09-642 (also LAPACK Working Note 219),
    May 24, 2009.

    @ingroup magma_zgeev_aux
    ********************************************************************/
extern "C" magma_int_t
magma_zlahr2(
    magma_int_t n, magma_int_t k,