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Update decompression_single_color! for star coloring #217

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Merged
gdalle merged 4 commits into from
Mar 31, 2025
Merged

Update decompression_single_color! for star coloring #217

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1b5bf48
Update decompression_single_color! for star coloring
amontoison Mar 31, 2025
11ae975
Remove the vector spokes
amontoison Mar 31, 2025
9e3595c
Merge branch 'main' into amontoison-patch-2
gdalle Mar 31, 2025
93ae6ff
Update src/decompression.jl
gdalle Mar 31, 2025
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57 changes: 13 additions & 44 deletions src/coloring.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -87,7 +87,6 @@ function star_coloring(g::AdjacencyGraph, order::AbstractOrder, postprocessing::
star = Dict{Tuple{Int,Int},Int}()
sizehint!(star, ne)
hub = Int[] # one hub for each star, including the trivial ones
nb_spokes = Int[] # number of spokes for each star
vertices_in_order = vertices(g, order)

for v in vertices_in_order
Expand Down Expand Up @@ -119,9 +118,9 @@ function star_coloring(g::AdjacencyGraph, order::AbstractOrder, postprocessing::
break
end
end
_update_stars!(star, hub, nb_spokes, g, v, color, first_neighbor)
_update_stars!(star, hub, g, v, color, first_neighbor)
end
star_set = StarSet(star, hub, nb_spokes)
star_set = StarSet(star, hub)
if postprocessing
# Reuse the vector forbidden_colors to compute offsets during post-processing
postprocess!(color, star_set, g, forbidden_colors)
Expand All @@ -143,30 +142,6 @@ struct StarSet
star::Dict{Tuple{Int,Int},Int}
"a mapping from star indices to their hub (undefined hubs for single-edge stars are the negative value of one of the vertices, picked arbitrarily)"
hub::Vector{Int}
"a mapping from star indices to the vector of their spokes"
spokes::Vector{Vector{Int}}
end

function StarSet(star::Dict{Tuple{Int,Int},Int}, hub::Vector{Int}, nb_spokes::Vector{Int})
# Create a list of spokes for each star, preallocating their sizes based on nb_spokes
spokes = [Vector{Int}(undef, ns) for ns in nb_spokes]

# Reuse nb_spokes as counters to track the current index while filling the spokes
fill!(nb_spokes, 0)

for ((i, j), s) in pairs(star)
h = abs(hub[s])
nb_spokes[s] += 1
index = nb_spokes[s]

# Assign the non-hub vertex (spoke) to the correct position in spokes
if i == h
spokes[s][index] = j
elseif j == h
spokes[s][index] = i
end
end
return StarSet(star, hub, spokes)
end

_sort(u, v) = (min(u, v), max(u, v))
Expand All @@ -193,7 +168,6 @@ function _update_stars!(
# modified
star::Dict{<:Tuple,<:Integer},
hub::AbstractVector{<:Integer},
nb_spokes::AbstractVector{<:Integer},
# not modified
g::AdjacencyGraph,
v::Integer,
Expand All @@ -209,7 +183,6 @@ function _update_stars!(
wx = _sort(w, x)
star_wx = star[wx]
hub[star_wx] = w # this may already be true
nb_spokes[star_wx] += 1
star[vw] = star_wx
x_exists = true
break
Expand All @@ -221,11 +194,9 @@ function _update_stars!(
vq = _sort(v, q)
star_vq = star[vq]
hub[star_vq] = v # this may already be true
nb_spokes[star_vq] += 1
star[vw] = star_vq
else # vw forms a new star
push!(hub, -max(v, w)) # star is trivial (composed only of two vertices) so we set the hub to a negative value, but it allows us to choose one of the two vertices
push!(nb_spokes, 1)
star[vw] = length(hub)
end
end
Expand Down Expand Up @@ -586,7 +557,7 @@ function postprocess!(

if star_or_tree_set isa StarSet
# only the colors of the hubs are used
(; hub, spokes) = star_or_tree_set
(; star, hub) = star_or_tree_set
nb_trivial_stars = 0

# Iterate through all non-trivial stars
Expand All @@ -601,19 +572,17 @@ function postprocess!(

# Process the trivial stars (if any)
if nb_trivial_stars > 0
for s in eachindex(hub)
j = hub[s]
if j < 0
i = spokes[s][1]
j = abs(j)
if color_used[color[i]]
# Make i the hub to avoid possibly adding one more used color
# Switch it with the (only) spoke
hub[s] = i
spokes[s][1] = j
for ((i, j), s) in pairs(star)
h = hub[s]
if h < 0
h = abs(h)
spoke = i == h ? j : i
if color_used[color[spoke]]
# Switch the hub and the spoke to possibly avoid adding one more used color
hub[s] = spoke
else
# Keep j as the hub
color_used[color[j]] = true
# Keep the current hub
color_used[color[h]] = true
end
end
end
Expand Down
42 changes: 21 additions & 21 deletions src/decompression.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -455,30 +455,30 @@ function decompress_single_color!(
result::StarSetColoringResult,
uplo::Symbol=:F,
)
(; ag, color, group, star_set) = result
(; hub, spokes) = star_set
(; ag, compressed_indices, group) = result
(; S) = ag
uplo == :F && check_same_pattern(A, S)

# Recover the diagonal coefficients of A
if has_diagonal(ag)
for i in group[c]
if !iszero(S[i, i])
A[i, i] = b[i]
end
end
end

# Recover the off-diagonal coefficients of A
for s in eachindex(hub, spokes)
j = abs(hub[s])
if color[j] == c
for i in spokes[s]
if in_triangle(i, j, uplo)
A[i, j] = b[i]
end
if in_triangle(j, i, uplo)
A[j, i] = b[i]
offset = (c - 1) * S.n
lower_index = offset + 1
upper_index = c * S.n
rvS = rowvals(S)
for j in group[c]
for k in nzrange(S, j)
if lower_index <= compressed_indices[k] <= upper_index
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l = compressed_indices[k] - offset
i = rvS[k]
if i == j
# Recover the diagonal coefficients of A
A[i, i] = b[l]
else
# Recover the off-diagonal coefficients of A
if in_triangle(i, j, uplo)
A[i, j] = b[l]
end
if in_triangle(j, i, uplo)
A[j, i] = b[l]
end
end
end
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end
Expand Down
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