Qiskit / rustworkx / 9301444525

94%

Build Type

push

github

Committed by web-flow

Commit Message

Add "saturation first" and "independent set" greedy node coloring strategies (#1138)

This PR adds two more standard coloring strategies to greedy node/edge coloring functions graph_greedy_color and graph_greedy_edge_color.

In the literature the first strategy is known as "saturation", "DSATUR" or "SLF". We dynamically choose the vertex that has the largest number of different colors already assigned to its neighbors, and, in case of a tie, the vertex that has the largest number of uncolored neighbors.

The second strategy is known as "greedy independent sets" or "GIS". We greedily find independent subsets of the graph, and assign a different color to each of these subsets.

This addresses #1137, modulo the fact that there are quadrillions of different greedy node coloring algorithms, and each comes with trillion variations.

Both new strategies can be combined with preset_color_fn (for node coloring).

There is also a new Rust enum GreedyStrategy exposed as a python class that allows to specify which of the three currently supported greedy strategies is used. This is, calling the functions from the Python code would be as follows:

import rustworkx as rx

graph = rx.generators.generalized_petersen_graph(5, 2)

coloring = rx.graph_greedy_color(graph, greedy_strategy=rx.GreedyStrategy.Degree)
coloring = rx.graph_greedy_color(graph, greedy_strategy=rx.GreedyStrategy.Saturation)
coloring = rx.graph_greedy_color(graph, greedy_strategy=rx.GreedyStrategy.IndependentSet)
coloring = rx.graph_greedy_color(graph)
coloring = rx.graph_greedy_edge_color(graph)
coloring = rx.graph_greedy_edge_color(graph, greedy_strategy=rx.GreedyStrategy.Degree)
coloring = rx.graph_greedy_edge_color(graph, greedy_strategy=rx.GreedyStrategy.Saturation)
coloring = rx.graph_greedy_edge_color(graph, greedy_strategy=rx.GreedyStrategy.IndependentSet)

The greedy_graph_edge_color function has been also extended to support the preset_color_fn argument (though in ... (continued)

Run Details

191 of 200 new or added lines in 3 files covered. (95.5%)

42 existing lines in 2 files now uncovered.

17254 of 18007 relevant lines covered (95.82%)

1174014.85 hits per line