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Fix union-find weight updates #32

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Merged
yomichi merged 1 commit into from
Jun 16, 2025
Merged

Fix union-find weight updates #32

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4 changes: 2 additions & 2 deletions src/model/common/union_find.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -56,7 +56,7 @@ const root! = root_path_halving!
@doc doc"""
unify!(u, n1, n2)

Connects `n1` and `n2` nodes and returns the root.
Connects `n1` and `n2` nodes using union by weight and returns the root.
"""
function unify!(u::UnionFind, n1::Integer, n2::Integer)
r1 = root!(u, n1)
Expand All @@ -67,7 +67,7 @@ function unify!(u::UnionFind, n1::Integer, n2::Integer)
r1, r2 = r2, r1
end
u.parents[r2] = r1
u.weights[r2] += u.weights[r1]
u.weights[r1] += u.weights[r2]
end
return r1
end
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3 changes: 2 additions & 1 deletion test/runtests.jl
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Expand Up @@ -12,7 +12,8 @@ const alpha = 0.001
filenames = ["observable.jl",
"classical.jl",
"quantum.jl",
"checkpoint.jl"]
"checkpoint.jl",
"union_find.jl"]
for filename in filenames
t = @elapsed include(filename)
println("$(filename): $t sec")
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23 changes: 23 additions & 0 deletions test/union_find.jl
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@@ -0,0 +1,23 @@
using Test
using SpinMonteCarlo

@testset "unify!" begin
uf = UnionFind(0)
addnode!(uf) # node 1
addnode!(uf) # node 2
addnode!(uf) # node 3
addnode!(uf) # node 4

# merge two pairs
r12 = unify!(uf, 1, 2)
r34 = unify!(uf, 3, 4)
@test uf.weights[r12] == 2
@test uf.weights[r34] == 2
@test uf.nclusters == 2

# merge the resulting sets
r = unify!(uf, 1, 3)
@test r == SpinMonteCarlo.root!(uf, 2) == SpinMonteCarlo.root!(uf, 4)
@test uf.weights[r] == 4
@test uf.nclusters == 1
end
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