>>> from scipy.sparse import coo_matrix
>>> sigma_m = np.array([[0, 1], [0, 0]])
>>> sp_m = graph.constant_sparse_pwc_operator(duration=0.1, operator=coo_matrix(sigma_m))
>>> graph.sparse_pwc_hermitian_part(sp_m)
<SparsePwc: operation_name="sparse_pwc_hermitian_part", value_shape=(2, 2)>