let printers = [
Obj.magic (Ldot (Lident "Owl_dense_real", "pp_dsmat"));
Obj.magic (Ldot (Lident "Owl_dense_complex", "pp_dsmat"));
Obj.magic (Ldot (Lident "Owl_sparse_real", "pp_spmat"));
Obj.magic (Ldot (Lident "Owl_sparse_complex", "pp_spmat"));
]