Merge pull request #20 from ArrogantGao/xz/new_selector

Added a new selector `MinBoundaryHighDegreeSelector`

lib/OptimalBranchingMIS/src/OptimalBranchingMIS.jl

@@ -8,7 +8,7 @@ using GenericTensorNetworks
 
 export MISProblem
 export MISReducer, XiaoReducer
-export MinBoundarySelector
+export MinBoundarySelector, MinBoundaryHighDegreeSelector
 export TensorNetworkSolver
 export NumOfVertices, D3Measure
 

lib/OptimalBranchingMIS/src/interfaces.jl

@@ -1,36 +1,36 @@
 """
-    mis_size(g::AbstractGraph; bs::BranchingStrategy = BranchingStrategy(table_solver = TensorNetworkSolver(), selector = MinBoundarySelector(2), measure=D3Measure()), reducer::AbstractReducer = MISReducer())
+    mis_size(g::AbstractGraph; bs::BranchingStrategy = BranchingStrategy(table_solver = TensorNetworkSolver(), selector = MinBoundaryHighDegreeSelector(2, 6, 0), measure=D3Measure()), reducer::AbstractReducer = MISReducer())
 
 Calculate the size of the Maximum Independent Set (MIS) for a given graph.
 
 ### Arguments
 - `g::AbstractGraph`: The graph for which the MIS size is to be calculated.
-- `bs::BranchingStrategy`: (optional) The branching strategy to be used. Defaults to a strategy using `table_solver=TensorNetworkSolver`, `selector=MinBoundarySelector(2)`, and `measure=D3Measure`.
+- `bs::BranchingStrategy`: (optional) The branching strategy to be used. Defaults to a strategy using `table_solver=TensorNetworkSolver`, `selector=MinBoundaryHighDegreeSelector(2, 6, 0)`, and `measure=D3Measure`.
 - `reducer::AbstractReducer`: (optional) The reducer to be applied. Defaults to `MISReducer`.
 
 ### Returns
 - An integer representing the size of the Maximum Independent Set for the given graph.
 """
-function mis_size(g::AbstractGraph; bs::BranchingStrategy = BranchingStrategy(table_solver = TensorNetworkSolver(), selector = MinBoundarySelector(2), measure=D3Measure()), reducer=MISReducer())
+function mis_size(g::AbstractGraph; bs::BranchingStrategy = BranchingStrategy(table_solver = TensorNetworkSolver(), selector = MinBoundaryHighDegreeSelector(2, 6, 0), measure=D3Measure()), reducer=MISReducer())
     p = MISProblem(g)
     res = branch_and_reduce(p, bs, reducer, MaxSize)
     return res.size
 end
 
 """
-    mis_branch_count(g::AbstractGraph; bs::BranchingStrategy = BranchingStrategy(table_solver = TensorNetworkSolver(), selector = MinBoundarySelector(2), measure=D3Measure()), reducer=MISReducer())
+    mis_branch_count(g::AbstractGraph; bs::BranchingStrategy = BranchingStrategy(table_solver = TensorNetworkSolver(), selector = MinBoundaryHighDegreeSelector(2, 6, 0), measure=D3Measure()), reducer=MISReducer())
 
 Calculate the size and the number of branches of the Maximum Independent Set (MIS) for a given graph.
 
 ### Arguments
 - `g::AbstractGraph`: The graph for which the MIS size and the number of branches are to be calculated.
-- `bs::BranchingStrategy`: (optional) The branching strategy to be used. Defaults to a strategy using `table_solver=TensorNetworkSolver`, `selector=MinBoundarySelector(2)`, and `measure=D3Measure`.
+- `bs::BranchingStrategy`: (optional) The branching strategy to be used. Defaults to a strategy using `table_solver=TensorNetworkSolver`, `selector=MinBoundaryHighDegreeSelector(2, 6, 0)`, and `measure=D3Measure`.
 - `reducer::AbstractReducer`: (optional) The reducer to be applied. Defaults to `MISReducer`.
 
 ### Returns
 - A tuple `(size, count)` where `size` is the size of the Maximum Independent Set and `count` is the number of branches.
 """
-function mis_branch_count(g::AbstractGraph; branching_strategy::BranchingStrategy = BranchingStrategy(table_solver = TensorNetworkSolver(), selector = MinBoundarySelector(2), measure=D3Measure()), reducer=MISReducer())
+function mis_branch_count(g::AbstractGraph; branching_strategy::BranchingStrategy = BranchingStrategy(table_solver = TensorNetworkSolver(), selector = MinBoundaryHighDegreeSelector(2, 6, 0), measure=D3Measure()), reducer=MISReducer())
     p = MISProblem(g)
     res = branch_and_reduce(p, branching_strategy, reducer, MaxSizeBranchCount)
     return (res.size, res.count)

lib/OptimalBranchingMIS/src/selector.jl

@@ -16,22 +16,61 @@ function OptimalBranchingCore.select_variables(p::MISProblem, m::M, selector::Mi
     @assert nv(g) > 0
     kneighbor = selector.k
 
+    local vs_min
+
+    novs_min = nv(g)
+    for v in 1:nv(g)
+        vs, ovs = neighbor_cover(g, v, kneighbor)
+        if length(ovs) < novs_min
+            vs_min = vs
+            novs_min = length(ovs)
+        end
+    end
+    return vs_min
+end
+
+"""
+    struct MinBoundaryHighDegreeSelector <: AbstractVertexSelector
+
+The `MinBoundaryHighDegreeSelector` struct represents a strategy:
+    - if exists a vertex with degree geq high_degree_threshold, then select it and its k-degree neighbors.
+    - otherwise, select a subgraph with the minimum number of open vertices by k-layers of neighbors.
+
+# Fields
+- `kb::Int`: The number of layers of neighbors to consider when selecting the subgraph.
+- `hd::Int`: The threshold of degree for a vertex to be selected.
+- `kd::Int`: The number of layers of neighbors to consider when selecting the subgraph.
+
+"""
+struct MinBoundaryHighDegreeSelector <: AbstractSelector
+    kb::Int # k-boundary
+    hd::Int # high-degree threshold
+    kd::Int # k-degree
+end
+
+function OptimalBranchingCore.select_variables(p::MISProblem, m::M, selector::MinBoundaryHighDegreeSelector) where{M<:AbstractMeasure}
+    g = p.g
+    @assert nv(g) > 0
+    boundary_neighbor = selector.kb
+    high_degree_threshold = selector.hd
+    high_degree_neighbor = selector.kd
+
     local vs_min
     # if exists a vertex with degree geq 6, then select it and it 1st-order neighbors.
     for v in 1:nv(g)
-        if degree(g, v) ≥ 6
-            vs_min =  neighbor_cover(g, v, 1)[1]
+        if degree(g, v) ≥ high_degree_threshold
+            vs_min = neighbor_cover(g, v, high_degree_neighbor)[1]
             return vs_min
         end
     end
 
     novs_min = nv(g)
     for v in 1:nv(g)
-        vs, ovs = neighbor_cover(g, v, kneighbor)
+        vs, ovs = neighbor_cover(g, v, boundary_neighbor)
         if length(ovs) < novs_min
             vs_min = vs
             novs_min = length(ovs)
         end
     end
     return vs_min
-end
+end

lib/OptimalBranchingMIS/test/branch.jl

@@ -11,8 +11,8 @@ using Test, Random
             mis_exact = mis2(EliminateGraph(g))
             p = MISProblem(g)
 
-            for set_cover_solver in [IPSolver(10, false), LPSolver(10, false)], measure in [D3Measure(), NumOfVertices()], reducer in [NoReducer(), MISReducer(), XiaoReducer()], prune_by_env in [true, false]
-                branching_strategy = BranchingStrategy(; set_cover_solver, table_solver=TensorNetworkSolver(; prune_by_env), selector=MinBoundarySelector(2), measure)
+            for set_cover_solver in [IPSolver(10, false), LPSolver(10, false)], measure in [D3Measure(), NumOfVertices()], reducer in [NoReducer(), MISReducer(), XiaoReducer()], prune_by_env in [true, false], selector in [MinBoundarySelector(2), MinBoundaryHighDegreeSelector(2, 6, 0), MinBoundaryHighDegreeSelector(2, 6, 1)]
+                branching_strategy = BranchingStrategy(; set_cover_solver, table_solver=TensorNetworkSolver(; prune_by_env), selector=selector, measure)
                 res = branch_and_reduce(p, branching_strategy, reducer, MaxSize)
                 res_count = branch_and_reduce(p, branching_strategy, reducer, MaxSizeBranchCount)