Create and modify a subgraph

Create a subgraph

There are three methods provided for creating a subgraph from the graph:

1. filter by nodes (“nodes”)

2. filter by node callable parameters (“inputs”)

3. filter by node callable returns (“outputs”)

Note

The filtered subgraph is a view of the original graph, and they are frozen.

If we filter the graph by the output “log_xy”, the node “function node” is excluded. The resulting subgraph can be built into models (the graph is defined the same as README.rst):

H = G.subgraph(outputs=["log_xy"])
model = Model("model", H, MemHandler)

>>> print(H.nodes)
['add', 'log']

The filtering is useful if we only want to create a model callable for only part of the graph.

Create a model based on a subgraph

Subgraphing is also helpful if we apply modifiers to part of the graph. For example, we want to loop a variable that only part of the subgraph uses. Here, we loop the “log_base” parameter from the README example. replace_subgraph outputs a new graph.

H = G.subgraph(inputs=["log_base"])
loop_node = Model(
    "loop_submodel",
    H,
    handler=MemHandler,
    modifiers=[loop_input("log_base"})],
)
looped_graph = G.replace_subgraph(H, Node("loop_node", loop_node, output="looped_z"))

looped_model = Model("looped_model", looped_graph, loop_node.handler)

The steps:

1. Filter the graph with G.subgraph(inputs=...).

2. Create a subgraph model with Model and loop modifiers.

3. Update the graph with the subgraph nodes object loop_node with

   replace_subgraph. Use “output” to specify the output name of the subgraph node.

4. Build the model for the graph with Model. The handler is the same as

   the loop_node.