is the order of print_graph guarateed to be the same?

Development
1

@szhorvat
It’s in tests/unit/test_utilities.inc . It uses IGRAPH_FROM(graph, i), IGRAPH_TO(graph, i), which use the from and to fields of the igraph_s struct. These don’t seem to have a guaranteed order. If so, tests could fail in the future if internals change, even though the correct graph is printed.

2

The order of the edges should be preserved regardless of the exact implementation of igraph_t. Internally, there are some sorted indices, but this does not (and should not) affect the actual edge index.

3

Ah, I think I asked the wrong question.

If I call igraph_small with two different edge orders, they also print out differently, I should have just checked that:

directed: true
vcount: 3
edges: {
0 1
0 2
}
directed: true
vcount: 3
edges: {
0 2
0 1
}

But suppose I am now testing igraph_full_citation for example. If I use print_graph to check it’s output, and at some point igraph_full_citation changes internally to output the edges in a different order, the test fails, even though nothing’s wrong. This would be prevented by ordering the output.

So my suggestion would be to order the output of print_graph so tests are more stable. Or am I missing something?

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4

Yes, this is a good suggestion. I’ll look into it.

Something related: I also want to add a new public function that verifies that two graphs are the same (not isomorphic, but having exactly the same edges, i.e. 1-2, 2-3 and 2-3, 1-2 are the same, but 1-3, 3-2 is different). I briefly discussed this with @tamas about a month ago.

5

That would also solve my current issue completely :slight_smile:

6

@GroteGnoom I have now added a function, print_graph_canon(), that outputs the graph in a canonical representation.

Something unrelated: You might be interested in looking at code coverage reports, Generating test coverage reports · igraph/igraph Wiki · GitHub

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