Run conquer algorithm in TreeSearch only if conquer_output of the n…

…ode is empty (#1076)

* Get rid of Node.conquerwasrun, instead we maintain conquer_output
Now, we run conquer only if conquer_output is empty

* Correction to pass the tests

* Forgot to commit a file

src/Algorithm/branching/branchingalgo.jl

@@ -274,7 +274,7 @@ end
 
 function Branching.eval_child_of_candidate!(child, phase::Branching.AbstractStrongBrPhaseContext, ip_primal_sols_found, env, reform, input)    
     child_state = OptimizationState(getmaster(reform))
-    child.optstate = child_state
+    child.conquer_output = child_state
 
     # In the `ip_primal_sols_found`, we maintain all the primal solutions found during the 
     # strong branching procedure but also the best primal bound found so far (in the whole optimization).
@@ -284,11 +284,9 @@ function Branching.eval_child_of_candidate!(child, phase::Branching.AbstractStro
         units_to_restore = Branching.get_units_to_restore_for_conquer(phase)
         restore_from_records!(units_to_restore, child.records)
         conquer_input = ConquerInputFromSb(Branching.get_global_primal_handler(input), child, units_to_restore)
-        child_state = run!(Branching.get_conquer(phase), env, reform, conquer_input)
-        child.optstate = child_state
+        child.conquer_output = run!(Branching.get_conquer(phase), env, reform, conquer_input)
         TreeSearch.set_records!(child, create_records(reform))
     end
-    child.conquerwasrun = true
 
     # Store new primal solutions found during the evaluation of the child.
     add_ip_primal_sols!(ip_primal_sols_found, get_ip_primal_sols(child_state)...)

src/Algorithm/branching/printer.jl

@@ -39,7 +39,7 @@ function Branching.perform_branching_phase!(candidates, cand_children, phase::Ph
         @printf " (lhs=%.4f) : [" Branching.get_lhs(candidate)
         for (node_index, node) in enumerate(children)
             node_index > 1 && print(",")            
-            @printf "%10.4f" getvalue(get_lp_primal_bound(node.optstate))
+            @printf "%10.4f" getvalue(get_lp_primal_bound(node.conquer_output))
         end
         @printf "], score = %10.4f\n" score
     end

src/Algorithm/branching/sbnode.jl

@@ -11,27 +11,21 @@ mutable struct SbNode <: TreeSearch.AbstractNode
     # There information are printed by the StrongBranchingPrinter.
     # These information will be then transfered to the B&B algorithm when instantating the
     # node of the tree search.
-    optstate::OptimizationState
+    conquer_output::Union{Nothing, OptimizationState}
 
-    var_name::String
     branchdescription::String
+    ip_dual_bound::Bound
     records::Records
-    conquerwasrun::Bool
     function SbNode(
-        reform::Reformulation, depth, var_name::String, branch_description::String, records::Records, input
+        depth, branch_description::String, ip_dual_bound::Bound, records::Records
     )
-        node_state = OptimizationState(
-            getmaster(reform);
-            ip_dual_bound = get_ip_dual_bound(Branching.get_conquer_opt_state(input))
-        )
-        return new(depth, node_state, var_name, branch_description, records, false)
+        return new(depth, nothing, branch_description, ip_dual_bound, records)
     end
 end
 
 getdepth(n::SbNode) = n.depth
 
 TreeSearch.set_records!(n::SbNode, records) = n.records = records
 TreeSearch.get_branch_description(n::SbNode) = n.branchdescription
-get_var_name(n::SbNode) = n.var_name
 TreeSearch.isroot(n::SbNode) = false
 Branching.isroot(n::SbNode) = TreeSearch.isroot(n)

src/Algorithm/branching/scores.jl

@@ -4,7 +4,7 @@ function Branching.compute_score(::ProductScore, children, input)
     parent = Branching.get_conquer_opt_state(input)
     parent_lp_dual_bound = get_lp_dual_bound(parent)
     parent_ip_primal_bound = get_ip_primal_bound(parent)
-    children_lp_primal_bounds = get_lp_primal_bound.(getfield.(children, Ref(:optstate)))
+    children_lp_primal_bounds = get_lp_primal_bound.(getfield.(children, Ref(:conquer_output)))
     return _product_score(parent_lp_dual_bound, parent_ip_primal_bound, children_lp_primal_bounds)
 end
 
@@ -14,7 +14,7 @@ function Branching.compute_score(::TreeDepthScore, children, input)
     parent = Branching.get_conquer_opt_state(input)
     parent_lp_dual_bound = get_lp_dual_bound(parent)
     parent_ip_primal_bound = get_ip_primal_bound(parent)
-    children_lp_primal_bounds = get_lp_primal_bound.(getfield.(children, :optstate))
+    children_lp_primal_bounds = get_lp_primal_bound.(getfield.(children, :conquer_output))
     return _tree_depth_score(parent_lp_dual_bound, parent_ip_primal_bound, children_lp_primal_bounds)
 end
 

src/Algorithm/branching/single_var_branching.jl

@@ -45,6 +45,8 @@ function Branching.generate_children!(
     units_to_restore = get_branching_candidate_units_usage(candidate, reform)
     d = Branching.get_parent_depth(input)
 
+    parent_ip_dual_bound = get_ip_dual_bound(Branching.get_conquer_opt_state(input))
+
     # adding the first branching constraints
     restore_from_records!(units_to_restore, Branching.parent_records(input))
     setconstr!(
@@ -57,7 +59,7 @@ function Branching.generate_children!(
         members = Dict{VarId,Float64}(candidate.varid => 1.0)
     )
     child1description = candidate.varname * ">=" * string(ceil(lhs))
-    child1 = SbNode(reform, d+1, candidate.varname, child1description, create_records(reform), input)
+    child1 = SbNode(d+1, child1description, parent_ip_dual_bound, create_records(reform))
 
     # adding the second branching constraints
     restore_from_records!(units_to_restore, Branching.parent_records(input))
@@ -71,7 +73,7 @@ function Branching.generate_children!(
         members = Dict{VarId,Float64}(candidate.varid => 1.0)
     )
     child2description = candidate.varname * "<=" * string(floor(lhs))
-    child2 = SbNode(reform, d+1, candidate.varname, child2description, create_records(reform), input)
+    child2 = SbNode(d+1, child2description, parent_ip_dual_bound, create_records(reform))
 
     return [child1, child2]
 end

src/Algorithm/treesearch.jl

@@ -166,10 +166,13 @@ function TreeSearch.children(space::AbstractColunaSearchSpace, current::TreeSear
     # Else we run the conquer algorithm.
     # This algorithm has the responsibility to check whether the node is pruned.
     reform = get_reformulation(space)
-    conquer_alg = get_conquer(space)
-    conquer_input = get_input(conquer_alg, space, current)
-    conquer_output = run!(conquer_alg, env, reform, conquer_input)
-    after_conquer!(space, current, conquer_output) # callback to do some operations after the conquer.
+    conquer_output = TreeSearch.get_conquer_output(current)
+    if conquer_output === nothing
+        conquer_alg = get_conquer(space)
+        conquer_input = get_input(conquer_alg, space, current)
+        conquer_output = run!(conquer_alg, env, reform, conquer_input)         
+        after_conquer!(space, current, conquer_output) # callback to do some operations after the conquer.
+    end
     # Build the divide input from the conquer output
     divide_alg = get_divide(space)
     divide_input = get_input(divide_alg, space, current, conquer_output)

src/Algorithm/treesearch/branch_and_bound.jl

@@ -26,15 +26,14 @@ mutable struct Node <: TreeSearch.AbstractNode
     # Information to restore the reformulation after the creation of the node (e.g. creation
     # of the branching constraint) or its partial evaluation (e.g. strong branching).
     records::Records
-
-    conquerwasrun::Bool # TODO: rename: full_evaluation (?)
 end
 
 getdepth(n::Node) = n.depth
 
 TreeSearch.isroot(n::Node) = n.depth == 0
 Branching.isroot(n::Node) = TreeSearch.isroot(n)
 TreeSearch.set_records!(n::Node, records) = n.records = records
+TreeSearch.get_conquer_output(n::Node) = n.conquer_output
 
 TreeSearch.get_branch_description(n::Node) = n.branchdescription # printer
 
@@ -45,10 +44,9 @@ TreeSearch.get_priority(::TreeSearch.BestDualBoundStrategy, n::Node) = n.ip_dual
 
 # TODO move
 function Node(node::SbNode)
-    ip_dual_bound = get_ip_dual_bound(node.optstate)
     return Node(
-        node.depth, node.branchdescription, node.optstate, ip_dual_bound,
-        node.records, node.conquerwasrun
+        node.depth, node.branchdescription, node.conquer_output, node.ip_dual_bound,
+        node.records
     )
 end
 
@@ -203,7 +201,7 @@ end
 function TreeSearch.new_root(sp::BaBSearchSpace, input)
     nodestate = OptimizationState(getmaster(sp.reformulation), input, false, false)
     return Node(
-        0, "", nothing, get_ip_dual_bound(nodestate), create_records(sp.reformulation), false
+        0, "", nothing, get_ip_dual_bound(nodestate), create_records(sp.reformulation)
     )
 end
 
@@ -215,7 +213,6 @@ function after_conquer!(space::BaBSearchSpace, current, conquer_output)
         store_ip_primal_sol!(space.inc_primal_manager, sol)
     end
     current.records = create_records(space.reformulation)
-    current.conquerwasrun = true
     space.nb_nodes_treated += 1
 
     # Branch & Bound returns the primal LP & the dual solution found at the root node.

src/TreeSearch/TreeSearch.jl

@@ -39,6 +39,9 @@ abstract type AbstractNode end
 "Returns the priority of the node depending on the explore strategy."
 @mustimplement "Node" get_priority(::AbstractExploreStrategy, ::AbstractNode) = nothing
 
+"Returns the conquer output if the conquer was already run for this node, otherwise returns nothing"
+get_conquer_output(::AbstractNode) = nothing
+
 ##### Additional methods for the node interface (needed by conquer)
 ## TODO: move outside TreeSearch module.
 @mustimplement "Node" set_records!(::AbstractNode, records) = nothing

test/unit/Branching/branching_default.jl

@@ -237,7 +237,7 @@ function test_strong_branching()
     # TODO: interface to register Records.
     records = Coluna.Algorithm.Records()
     node = Coluna.Algorithm.Node(
-        0, "", nothing, MathProg.DualBound(reform), records, false 
+        0, "", nothing, MathProg.DualBound(reform), records
     )
 
     global_primal_handler = Coluna.Algorithm.GlobalPrimalBoundHandler(reform)

test/unit/TreeSearch/treesearch.jl

@@ -138,7 +138,7 @@ end
 
 # constructs a real node from a LightNode, used in new_children to built real children from the minimal information contained in LightNode
 function Coluna.Algorithm.Node(node::LightNode)
-    return Coluna.Algorithm.Node(node.depth, " ", nothing, node.parent_ip_dual_bound, Coluna.Algorithm.Records(), false)
+    return Coluna.Algorithm.Node(node.depth, " ", nothing, node.parent_ip_dual_bound, Coluna.Algorithm.Records())
 end
 
 ## The candidates are passed as LightNodes and the current node is passed as a TestBaBNode. The method retrieves the inner nodes to run the native method new_children of branch_and_bound.jl, gets the result as a vector of Nodes and then re-built a solution as a vector of TestBaBNodes using the nodes ids contained in LightNode structures.