Implement google_matrix and binary operators

[eriknw]

These aren't super-optimized or super-clean, but are hopefully "good enough" for a while.

[eriknw]

@jim22k, test_intersection is raising, and it looks like code you added. Can you help? Note that I implemented intersection in this PR.

[jim22k]

Other than my comment above, this all looks good to me.

[eriknw]

Other than my comment above, this all looks good to me.

Thanks for reviewing! Thoughts on the failing test?

[jim22k]

Thoughts on the failing test?

I think the line:
if os.environ.get("NETWORKX_GRAPH_CONVERT", None) != "nx-loopback":
should instead be:
if os.environ.get("NETWORKX_GRAPH_CONVERT", None) is not None:

The point of that test is to check that nx._dispatch raises a TypeError when differently typed Graph objects are passed in. But we don't need to test that during auto dispatching tests.

Can you make that change in NetworkX and see if the tests pass? If so, please add that change to your NetworkX PR. Thanks!

[eriknw]

if os.environ.get("NETWORKX_GRAPH_CONVERT", None) is not None:

This doesn't work, b/c we convert networkx graphs (we always call e.g. to_graph). Should it instead be == "nx-loopback":? I still don't quite follow what's going on. Also, I think this ought to be broken out into its own test.

[jim22k]

Oops. Try this instead:

# Only test if not performing auto convert testing of backend implementations
if os.environ.get("NETWORKX_GRAPH_CONVERT", None) is None:

The goal is to only test this if we aren't doing auto convert testing.

[eriknw]

Merging. The test failure is understood--we are waiting on NetworkX PR to be merged.