Fix respectful_similar with SparsityPatternCSC (#299)

* Fix respectful_similar with SparsityPatternCSC

* Add test

* Fix format

* Add test

---------

Co-authored-by: Alexis Montoison <35051714+amontoison@users.noreply.github.com>

Author: blegat

src/graph.jl

@@ -32,6 +32,11 @@ SparseArrays.nnz(S::SparsityPatternCSC) = length(S.rowval)
 SparseArrays.rowvals(S::SparsityPatternCSC) = S.rowval
 SparseArrays.nzrange(S::SparsityPatternCSC, j::Integer) = S.colptr[j]:(S.colptr[j + 1] - 1)
 
+# Needed if using `coloring(::SparsityPatternCSC, ...)`
+function Base.similar(A::SparsityPatternCSC, ::Type{T}) where {T}
+    return SparseArrays.SparseMatrixCSC(A.m, A.n, A.colptr, A.rowval, similar(A.rowval, T))
+end
+
 """
     transpose(S::SparsityPatternCSC)
 

test/structured.jl

@@ -2,6 +2,7 @@ using ArrayInterface: ArrayInterface
 using BandedMatrices: BandedMatrix, brand
 using BlockBandedMatrices: BandedBlockBandedMatrix, BlockBandedMatrix
 using LinearAlgebra
+using SparseArrays
 using SparseMatrixColorings
 using Test
 
@@ -56,3 +57,19 @@ end;
         test_structured_coloring_decompression(A)
     end
 end;
+
+# See https://github.com/gdalle/SparseMatrixColorings.jl/pull/299
+@testset "SparsityPatternCSC $T" for T in [Int, Float32]
+    S = sparse(T[
+        0 0 1 1 0 1
+        1 0 0 0 1 0
+        0 1 0 0 1 0
+        0 1 1 0 0 0
+    ])
+    P = SparseMatrixColorings.SparsityPatternCSC(S)
+    problem = ColoringProblem()
+    algo = GreedyColoringAlgorithm()
+    result = coloring(P, problem, algo)
+    B = compress(S, result)
+    @test decompress(B, result) isa SparseMatrixCSC{T,Int}
+end;