Add more methods for coloring?

[amontoison]

In interface.jl we have:

function coloring(
    S::AbstractMatrix,
    ::ColoringProblem{:symmetric,:column,:direct},
    algo::GreedyColoringAlgorithm,
)
    ag = adjacency_graph(S)
    color, star_set = star_coloring(ag, algo.order)
    # TODO: handle star_set
    return DefaultColoringResult{:symmetric,:column,:direct}(S, color)
end

function coloring(
    S::AbstractMatrix,
    ::ColoringProblem{:symmetric,:column,:substitution},
    algo::GreedyColoringAlgorithm,
)
    ag = adjacency_graph(S)
    color, tree_set = acyclic_coloring(ag, algo.order)
    # TODO: handle tree_set
    return DefaultColoringResult{:symmetric,:column,:substitution}(S, color)
end

Should we also add:

function coloring(
    S::AbstractMatrix,
    ::ColoringProblem{:symmetric,:row,:direct},
    algo::GreedyColoringAlgorithm,
)
    ag = adjacency_graph(S)
    color, star_set = star_coloring(ag, algo.order)
    # TODO: handle star_set
    return DefaultColoringResult{:symmetric,:row,:direct}(S, color)
end

function coloring(
    S::AbstractMatrix,
    ::ColoringProblem{:symmetric,:row,:substitution},
    algo::GreedyColoringAlgorithm,
)
    ag = adjacency_graph(S)
    color, tree_set = acyclic_coloring(ag, algo.order)
    # TODO: handle tree_set
    return DefaultColoringResult{:symmetric,:row,:substitution}(S, color)
end

Alternative solution:
Should we add a :row_or_column entry to the partition, and only allow it if structure == :symmetric?

[gdalle]

For now let's impose that symmetric matrices are always colored and decompressed by columns. This minimizes the surface of error.

We should document it though.

[amontoison]

We can close the issue after an update of the documentation to specify that symmetric matrices are always colored and decompressed by columns.