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Zero-fill block_starts instead of leaving unstored slots undef #250

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Merged
dlfivefifty merged 1 commit into from
Sep 28, 2026
Merged

Zero-fill block_starts instead of leaving unstored slots undef #250

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3 changes: 2 additions & 1 deletion src/BlockSkylineMatrix.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,8 @@ checkbandwidths(N, M, l::AbstractVector{Int}, u::AbstractVector{Int}) =
function bb_blockstarts(ax, l::AbstractVector{Int}, u::AbstractVector{Int})
N,M = blocksize.(ax,1)
L,U = maximum(l), maximum(u)
b_start = BandedMatrix{Int}(undef, (N, M), (L, U))
# zero-filled so in-band slots for blocks outside a column's own band read as 0
b_start = BandedMatrix(Zeros{Int}(N, M), (L, U))
-L > U && return b_start

checkbandwidths(N, M, l, u)
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8 changes: 8 additions & 0 deletions test/test_blockskyline.jl
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Expand Up @@ -165,6 +165,14 @@ Random.seed!(0)
s = split(sprint(show, "text/plain", B), '\n')[2]
@test s == " 1 │ 0 0 │ ⋅ ⋅ ⋅ │ ⋅ ⋅ ⋅ ⋅"
end

@testset "block_starts" begin
# block (3,2) is in the band of block_starts but not stored, so must be 0
bs = BlockBandedMatrices.BlockSkylineSizes([2,3,4], [1,2,3], [2,0,0], [0,1,1])
@test Matrix(bs.block_starts) == [1 10 0;
3 12 20;
6 0 23]
end
end

end # module
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