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Merged
amontoison merged 1 commit into from
Nov 1, 2025
Merged

Add a file postprocessing.jl #275

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1 change: 1 addition & 0 deletions src/SparseMatrixColorings.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,7 @@ include("graph.jl")
include("forest.jl")
include("order.jl")
include("coloring.jl")
include("postprocessing.jl")
include("result.jl")
include("matrices.jl")
include("interface.jl")
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147 changes: 0 additions & 147 deletions src/coloring.jl
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Expand Up @@ -643,150 +643,3 @@ function TreeSet(

return TreeSet(reverse_bfs_orders, is_star, tree_edge_indices, nt)
end

## Postprocessing, mirrors decompression code

function postprocess!(
color::AbstractVector{<:Integer},
star_or_tree_set::Union{StarSet,TreeSet},
g::AdjacencyGraph,
offsets::AbstractVector{<:Integer},
)
S = pattern(g)
edge_to_index = edge_indices(g)
# flag which colors are actually used during decompression
nb_colors = maximum(color)
color_used = zeros(Bool, nb_colors)

# nonzero diagonal coefficients force the use of their respective color (there can be no neutral colors if the diagonal is fully nonzero)
if has_diagonal(g)
for i in axes(S, 1)
if !iszero(S[i, i])
color_used[color[i]] = true
end
end
end

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

# Iterate through all non-trivial stars
for s in eachindex(hub)
h = hub[s]
if h > 0
color_used[color[h]] = true
else
nb_trivial_stars += 1
end
end

# Process the trivial stars (if any)
if nb_trivial_stars > 0
rvS = rowvals(S)
for j in axes(S, 2)
for k in nzrange(S, j)
i = rvS[k]
if i > j
index_ij = edge_to_index[k]
s = star[index_ij]
h = hub[s]
if h < 0
h = abs(h)
spoke = h == j ? i : j
if color_used[color[spoke]]
# Switch the hub and the spoke to possibly avoid adding one more used color
hub[s] = spoke
else
# Keep the current hub
color_used[color[h]] = true
end
end
end
end
end
end
else
# only the colors of non-leaf vertices are used
(; reverse_bfs_orders, is_star, tree_edge_indices, nt) = star_or_tree_set
nb_trivial_trees = 0

# Iterate through all non-trivial trees
for k in 1:nt
# Position of the first edge in the tree
first = tree_edge_indices[k]

# Total number of edges in the tree
ne_tree = tree_edge_indices[k + 1] - first

# Check if we have more than one edge in the tree (non-trivial tree)
if ne_tree > 1
# Determine if the tree is a star
if is_star[k]
# It is a non-trivial star and only the color of the hub is needed
(_, hub) = reverse_bfs_orders[first]
color_used[color[hub]] = true
else
# It is not a star and both colors are needed during the decompression
(i, j) = reverse_bfs_orders[first]
color_used[color[i]] = true
color_used[color[j]] = true
end
else
nb_trivial_trees += 1
end
end

# Process the trivial trees (if any)
if nb_trivial_trees > 0
for k in 1:nt
# Position of the first edge in the tree
first = tree_edge_indices[k]

# Total number of edges in the tree
ne_tree = tree_edge_indices[k + 1] - first

# Check if we have exactly one edge in the tree
if ne_tree == 1
(i, j) = reverse_bfs_orders[first]
if color_used[color[i]]
# Make i the root to avoid possibly adding one more used color
# Switch it with the (only) leaf
reverse_bfs_orders[first] = (j, i)
else
# Keep j as the root
color_used[color[j]] = true
end
end
end
end
end

# if at least one of the colors is useless, modify the color assignments of vertices
if any(!, color_used)
num_colors_useless = 0

# determine what are the useless colors and compute the offsets
for ci in 1:nb_colors
if color_used[ci]
offsets[ci] = num_colors_useless
else
num_colors_useless += 1
end
end

# assign the neutral color to every vertex with a useless color and remap the colors
for i in eachindex(color)
ci = color[i]
if !color_used[ci]
# assign the neutral color
color[i] = 0
else
# remap the color to not have any gap
color[i] -= offsets[ci]
end
end
end
return color
end
146 changes: 146 additions & 0 deletions src/postprocessing.jl
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Original file line number Diff line number Diff line change
@@ -0,0 +1,146 @@
## Postprocessing

function postprocess!(
color::AbstractVector{<:Integer},
star_or_tree_set::Union{StarSet,TreeSet},
g::AdjacencyGraph,
offsets::AbstractVector{<:Integer},
)
S = pattern(g)
edge_to_index = edge_indices(g)
# flag which colors are actually used during decompression
nb_colors = maximum(color)
color_used = zeros(Bool, nb_colors)

# nonzero diagonal coefficients force the use of their respective color (there can be no neutral colors if the diagonal is fully nonzero)
if has_diagonal(g)
for i in axes(S, 1)
if !iszero(S[i, i])
color_used[color[i]] = true
end
end
end

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

# Iterate through all non-trivial stars
for s in eachindex(hub)
h = hub[s]
if h > 0
color_used[color[h]] = true
else
nb_trivial_stars += 1
end
end

# Process the trivial stars (if any)
if nb_trivial_stars > 0
rvS = rowvals(S)
for j in axes(S, 2)
for k in nzrange(S, j)
i = rvS[k]
if i > j
index_ij = edge_to_index[k]
s = star[index_ij]
h = hub[s]
if h < 0
h = abs(h)
spoke = h == j ? i : j
if color_used[color[spoke]]
# Switch the hub and the spoke to possibly avoid adding one more used color
hub[s] = spoke
else
# Keep the current hub
color_used[color[h]] = true
end
end
end
end
end
end
else
# only the colors of non-leaf vertices are used
(; reverse_bfs_orders, is_star, tree_edge_indices, nt) = star_or_tree_set
nb_trivial_trees = 0

# Iterate through all non-trivial trees
for k in 1:nt
# Position of the first edge in the tree
first = tree_edge_indices[k]

# Total number of edges in the tree
ne_tree = tree_edge_indices[k + 1] - first

# Check if we have more than one edge in the tree (non-trivial tree)
if ne_tree > 1
# Determine if the tree is a star
if is_star[k]
# It is a non-trivial star and only the color of the hub is needed
(_, hub) = reverse_bfs_orders[first]
color_used[color[hub]] = true
else
# It is not a star and both colors are needed during the decompression
(i, j) = reverse_bfs_orders[first]
color_used[color[i]] = true
color_used[color[j]] = true
end
else
nb_trivial_trees += 1
end
end

# Process the trivial trees (if any)
if nb_trivial_trees > 0
for k in 1:nt
# Position of the first edge in the tree
first = tree_edge_indices[k]

# Total number of edges in the tree
ne_tree = tree_edge_indices[k + 1] - first

# Check if we have exactly one edge in the tree
if ne_tree == 1
(i, j) = reverse_bfs_orders[first]
if color_used[color[i]]
# Make i the root to avoid possibly adding one more used color
# Switch it with the (only) leaf
reverse_bfs_orders[first] = (j, i)
else
# Keep j as the root
color_used[color[j]] = true
end
end
end
end
end

# if at least one of the colors is useless, modify the color assignments of vertices
if any(!, color_used)
num_colors_useless = 0

# determine what are the useless colors and compute the offsets
for ci in 1:nb_colors
if color_used[ci]
offsets[ci] = num_colors_useless
else
num_colors_useless += 1
end
end

# assign the neutral color to every vertex with a useless color and remap the colors
for i in eachindex(color)
ci = color[i]
if !color_used[ci]
# assign the neutral color
color[i] = 0
else
# remap the color to not have any gap
color[i] -= offsets[ci]
end
end
end
return color
end
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