def contract_path(path: Tuple[List[Tuple[int, int]]], nodes: Iterable[AbstractNode], output_edge_order: Sequence[Edge]) -> AbstractNode: """Contract `nodes` using `path`. Args: path: The contraction path as returned from `path_solver`. nodes: A collection of connected nodes. output_edge_order: A list of edges. Edges of the final node in `nodes` are reordered into `output_edge_order`; Returns: Final node after full contraction. """ edges = get_all_edges(nodes) for edge in edges: if not edge.is_disabled: #if its disabled we already contracted it if edge.is_trace(): contract_parallel(edge) if len(nodes) == 1: newnode = nodes[0].copy() for edge in nodes[0].edges: redirect_edge(edge, newnode, nodes[0]) return newnode.reorder_edges(output_edge_order) if len(path) == 0: return nodes for p in path: if len(p) > 1: a, b = p new_node = contract_between(nodes[a], nodes[b], allow_outer_product=True) nodes.append(new_node) nodes = utils.multi_remove(nodes, [a, b]) elif len(p) == 1: a = p[0] node = nodes.pop(a) new_node = contract_trace_edges(node) nodes.append(new_node) # if the final node has more than one edge, # output_edge_order has to be specified final_node = nodes[0] # nodes were connected, we checked this #some contractors miss trace edges final_node = contract_trace_edges(final_node) final_node.reorder_edges(output_edge_order) return final_node
def _base_nodes( nodes: Iterable[BaseNode], algorithm: utils.Algorithm, output_edge_order: Optional[Sequence[Edge]] = None) -> BaseNode: """Base method for all `opt_einsum` contractors. Args: nodes: A collection of connected nodes. algorithm: `opt_einsum` contraction method to use. output_edge_order: An optional list of edges. Edges of the final node in `nodes_set` are reordered into `output_edge_order`; if final node has more than one edge, `output_edge_order` must be pronvided. Returns: Final node after full contraction. """ nodes_set = set(nodes) check_connected(nodes_set) edges = get_all_edges(nodes_set) #output edge order has to be determinded before any contraction #(edges are refreshed after contractions) if output_edge_order is None: output_edge_order = list(get_subgraph_dangling(nodes)) if len(output_edge_order) > 1: raise ValueError( "The final node after contraction has more than " "one remaining edge. In this case `output_edge_order` " "has to be provided.") if set(output_edge_order) != get_subgraph_dangling(nodes): raise ValueError("output edges are not equal to the remaining " "non-contracted edges of the final node.") for edge in edges: if not edge.is_disabled: #if its disabled we already contracted it if edge.is_trace(): nodes_set.remove(edge.node1) nodes_set.add(contract_parallel(edge)) if len(nodes_set) == 1: # There's nothing to contract. return list(nodes_set)[0].reorder_edges(output_edge_order) # Then apply `opt_einsum`'s algorithm path, nodes = utils.get_path(nodes_set, algorithm) for a, b in path: new_node = nodes[a] @ nodes[b] nodes.append(new_node) nodes = utils.multi_remove(nodes, [a, b]) # if the final node has more than one edge, # output_edge_order has to be specified final_node = nodes[0] # nodes were connected, we checked this final_node.reorder_edges(output_edge_order) return final_node
def auto( nodes: BaseNode, output_edge_order: Optional[Sequence[Edge]] = None, memory_limit: Optional[int] = None, ignore_edge_order: bool = False) -> BaseNode: """Chooses one of the above algorithms according to network size. Default behavior is based on `opt_einsum`'s `auto` contractor. Args: nodes: A collection of connected nodes. output_edge_order: An optional list of edges. Edges of the final node in `nodes_set` are reordered into `output_edge_order`; if final node has more than one edge, `output_edge_order` must be provided. memory_limit: Maximum number of elements in an array during contractions. ignore_edge_order: An option to ignore the output edge order. Returns: Final node after full contraction. """ n = len(list(nodes)) #pytype thing _nodes = nodes if n <= 0: raise ValueError("Cannot contract empty tensor network.") if n == 1: if not ignore_edge_order: if output_edge_order is None: output_edge_order = list( (get_all_edges(_nodes) - get_all_nondangling(_nodes))) if len(output_edge_order) > 1: raise ValueError("The final node after contraction has more than " "one dangling edge. In this case `output_edge_order` " "has to be provided.") edges = get_all_nondangling(_nodes) if edges: final_node = contract_parallel(edges.pop()) else: final_node = list(_nodes)[0] final_node.reorder_edges(output_edge_order) if not ignore_edge_order: final_node.reorder_edges(output_edge_order) return final_node if n < 5: return optimal(nodes, output_edge_order, memory_limit, ignore_edge_order) if n < 7: return branch(nodes, output_edge_order, memory_limit, ignore_edge_order) if n < 9: return branch(nodes, output_edge_order, memory_limit, nbranch=2, ignore_edge_order=ignore_edge_order) if n < 15: return branch(nodes, output_edge_order, nbranch=1, ignore_edge_order=ignore_edge_order) return greedy(nodes, output_edge_order, memory_limit, ignore_edge_order)
def contract_trace_edges(node: BaseNode) -> BaseNode: """ contract all trace edges of `node`. Args: node: A `BaseNode` obejct Returns: A new `BaseNode` obtained from contracting all trace edges. Raises: ValueError: If `node` has no trace edges """ for edge in node.edges: if edge.is_trace(): return contract_parallel(edge) raise ValueError('`node` has no trace edges')
def contract_trace_edges(node: AbstractNode) -> AbstractNode: """contract all trace edges of `node`. Args: node: A `AbstractNode` object. Returns: A new `AbstractNode` obtained from contracting all trace edges. """ res = node for edge in res.edges: if edge.is_trace(): res = contract_parallel(edge) break return res