Method clear

deps/GraphBLAS/CUDA/test/dataFactory.hpp:75–77

     uint64_t get_zombie_count() { return mat->nzombies;}

     void clear() {
        GRB_TRY (GrB_Matrix_clear (mat)) ;
     }

     void alloc() {
         GrB_Type type = cuda::jit::to_grb_type<T>();