Add Context-Free Path Query Algorithm for the Reachability Problem

[homka122]

Implementation of Context-Free Path Query Algorithm

This pull request adds an implementation of the Context-Free Path Query algorithm for solving the reachability problem using linear algebra. This algorithm was presented in the work available at this link.

Overview

The algorithm takes as input an edge-labeled graph and a context-free grammar, and it outputs all pairs of vertices between which there is at least one path such that the concatenation of edge labels forms a word in the language generated by the grammar.

Inputs

• Context-Free Grammar: An array of rules representing the context-free grammar.
• Graph: The graph is provided as a decomposition into adjacency matrices.

Output

The algorithm produces a set of matrices, each corresponding to a non-terminal of the grammar. For example, in the matrix A[k], the entry A[k][i, j] is 1 if and only if there is a path from node i to node j whose edge labels form a word derivable from the non-terminal k of the CFG.

Additional Details

A new structure has been added to represent a rule of the context-free grammar in Weak Chomsky Normal Form.

For a full description of the algorithm, please refer to the original document.

[DrTimothyAldenDavis]

Thanks for the contribution!

The stable branch is one we rarely change though -- only after it undergoes a deeper review and documentation, version change, and so on. Can you move the pull request to the v1.2 branch?

[DrTimothyAldenDavis]

Looks great!

[homka122]

@DrTimothyAldenDavis Ready!

[DrTimothyAldenDavis]

I see a lot of minor conflicts with the v1.2 branch though. Can you resolve those first? It looks like most of them should stay unmodified in the v1.2 branch. Sorry for the hassle.

[homka122]

@DrTimothyAldenDavis Sure!

[homka122]

@DrTimothyAldenDavis Hi! I resolved all conflicts.

[DrTimothyAldenDavis]

I've been working on getting LAGraph v1.2 version polished, with the goal of a stable version release. I have the test coverage up to nearly 100%, but there are a few lines in the CFL method that aren't tested by the tests in test_CFL_reachability.c. I've tagged the untested lines of code in LAGraph_CFL_reachability.c with FIXMEs. Can you take a look?

[homka122]

I've been working on getting LAGraph v1.2 version polished, with the goal of a stable version release. I have the test coverage up to nearly 100%, but there are a few lines in the CFL method that aren't tested by the tests in test_CFL_reachability.c. I've tagged the untested lines of code in LAGraph_CFL_reachability.c with FIXMEs. Can you take a look?

Hi @DrTimothyAldenDavis. I’ve updated the code and test coverage is now at 100%!
You can check out the new pull request here: #291