D.Matval eye : int -> Owl_dense_matrix.D.matval tril : ?k:int -> Owl_dense_matrix.D.mat -> Owl_dense_matrix.D.matval triu : ?k:int -> Owl_dense_matrix.D.mat -> Owl_dense_matrix.D.matval diagm : ?k:int -> Owl_dense_matrix.D.mat -> Owl_dense_matrix.D.mat