Kneser Graph Generator

[valdaarhun]

New feature: Generation of kneser graphs.

Resolves #1876.

So far, I have only implemented functions to calculate $\binom{n}{k}$ and generate k-size subsets. I have made both functions static and put them in kneser.c. Please let me know if I should integrate them into iterators.c instead.

I think it'll be best to finalize the design and implementation of the above functions before implementing the actual graph generator.

[ntamas]

• igraph_i_generate_subsets does not have a return type; it should be igraph_error_t and you should wrap the inner igraph_vector_list_... call in an IGRAPH_CHECK() to make sure that error codes are handled and propagated correctly. You should return IGRAPH_SUCCESS from the function when you wish to terminate the recursion.
• Global variables should not be used; igraph_i_generate_subsets() should receive the vector list in which the subsets should be filled as a parameter.
• The nCk variable is redundant; you can just return the corresponding expression directly.
• genSubset is not defined; you probably meant igraph_i_generate_subsets(), right?

[valdaarhun]

• genSubset is not defined; you probably meant igraph_i_generate_subsets(), right?

Hi. You're right, my bad. I forgot to change the name while refactoring.

[codecov]

Codecov Report

Merging #2233 (98162c0) into master (0c735a3) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2233   +/-   ##
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  Coverage   83.54%   83.54%           
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  Files         376      376           
  Lines       61586    61586           
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  Hits        51450    51450           
  Misses      10136    10136           

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[szhorvat]

Just a note that it's strongly preferred to use non-recursive implementations. Recursive functions are prone to stack overflow. This has happened in the past.

[valdaarhun]

Hi. I thought I would just give an update here. I have made igraph_i_generate_subsets iterative. I am still working on making igraph_i_number_of_subsets iterative.

Edit: Both functions are now iterative.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.

[GroteGnoom]

What's the status of this PR? @valdaarhun are you waiting for us before you continue?

[valdaarhun]

Hi. Yes, I was waiting for feedback. I apologize for not sending a reminder, I got caught up with other work. I would like to resume working on this now.

[ntamas]

Since temp is an igraph_vector_int_t, you need to use the functions that take an igraph_vector_int_t. For instance, igraph_vector_int_resize() instead of igraph_vector_resize(), igraph_vector_int_update() instead of igraph_vector_update() and so on. I haven't checked the correctness of the algorithm yet, this just simply struck my eye.

I haven't checked the correctness of this function, this just simply struck my eye.

[valdaarhun]

Oh, I must have missed this. I'll fix it.

[GroteGnoom]

Hi. Yes, I was waiting for feedback. I apologize for not sending a reminder, I got caught up with other work. I would like to resume working on this now.

No apologies necessary 🙂
As Tamás noticed, your types are not completely correct.

If you add your file to src/CMakeLists.txt you can use CMake to build your code and see the warnings.
(You can also maybe set up your editor so you can see these warnings while coding.)

If you add the actual generator function (or maybe for now just something that tests your subset generator) you can also add some tests in /tests/unit/ and add it in tests/CMakeLists, so your code gets run. That's one basic way of getting some feedback on your code :)

If you have any further questions (like about using CMake) don't hesitate to ask.

[valdaarhun]

If you add your file to src/CMakeLists.txt you can use CMake to build your code and see the warnings. (You can also maybe set up your editor so you can see these warnings while coding.)

If you add the actual generator function (or maybe for now just something that tests your subset generator) you can also add some tests in /tests/unit/ and add it in tests/CMakeLists, so your code gets run. That's one basic way of getting some feedback on your code :)

Oh, that's nice. I'll definitely do this.

If you have any further questions (like about using CMake) don't hesitate to ask.

Sure thing. Thanks.