Implement solve_all for MiniZinc

src/optimize.jl

@@ -25,22 +25,22 @@ mutable struct Optimizer{T} <: MOI.AbstractOptimizer
     inner::Model{T}
     solver_status::String
     primal_objective::T
-    primal_solution::Dict{MOI.VariableIndex,T}
+    primal_solutions::Vector{Dict{MOI.VariableIndex,T}}
     options::Dict{String,Any}
     time_limit_sec::Union{Nothing,Float64}
     solve_time_sec::Float64
     function Optimizer{T}(solver::String) where {T}
         if solver == "chuffed"
             solver = Chuffed()
         end
-        primal_solution = Dict{MOI.VariableIndex,T}()
-        options = Dict{String,Any}("model_filename" => "")
+        primal_solutions = Dict{MOI.VariableIndex,T}[]
+        options = Dict{String,Any}("model_filename" => "", "num_solutions" => 1)
         return new(
             solver,
             Model{T}(),
             "",
             zero(T),
-            primal_solution,
+            primal_solutions,
             options,
             nothing,
             NaN,
@@ -78,11 +78,13 @@ function _run_minizinc(dest::Optimizer)
     output = joinpath(dir, "model.ozn")
     _stdout = joinpath(dir, "_stdout.txt")
     _minizinc_exe() do exe
-        cmd = if dest.time_limit_sec !== nothing
+        cmd = `$(exe) --solver $(dest.solver) --output-objective -o $(output) $(filename)`
+        if dest.time_limit_sec !== nothing
             limit = round(Int, 1_000 * dest.time_limit_sec::Float64)
-            `$(exe) --solver $(dest.solver) --output-objective --time-limit $limit -o $(output) $(filename)`
-        else
-            `$(exe) --solver $(dest.solver) --output-objective -o $(output) $(filename)`
+            cmd = `$cmd --time-limit $limit`
+        end
+        if dest.options["num_solutions"] > 1
+            cmd = `$cmd --num-solutions $(dest.options["num_solutions"])`
         end
         return run(pipeline(cmd, stdout = _stdout))
     end
@@ -115,7 +117,7 @@ function MOI.empty!(model::Optimizer{T}) where {T}
     empty!(model.inner.ext)
     model.solver_status = ""
     model.primal_objective = zero(T)
-    empty!(model.primal_solution)
+    empty!(model.primal_solutions)
     model.solve_time_sec = NaN
     return
 end
@@ -129,6 +131,9 @@ function MOI.get(model::Optimizer, attr::MOI.RawOptimizerAttribute)
 end
 
 function MOI.set(model::Optimizer, attr::MOI.RawOptimizerAttribute, value)
+    if attr.name == "num_solutions" && !(value isa Int && value >= 1)
+        throw(MOI.SetAttributeNotAllowed("value must be an `Int` that is >= 1"))
+    end
     model.options[attr.name] = value
     return
 end
@@ -172,7 +177,7 @@ end
 function MOI.optimize!(dest::Optimizer{T}, src::MOI.ModelLike) where {T}
     time_start = time()
     MOI.empty!(dest.inner)
-    empty!(dest.primal_solution)
+    empty!(dest.primal_solutions)
     index_map = MOI.copy_to(dest.inner, src)
     ret = _run_minizinc(dest)
     if !isempty(ret)
@@ -186,15 +191,23 @@ function MOI.optimize!(dest::Optimizer{T}, src::MOI.ModelLike) where {T}
                 MOI.get(dest.inner, MOI.VariableName(), x) => x for
                 x in MOI.get(src, MOI.ListOfVariableIndices())
             )
+            primal_solution = Dict{MOI.VariableIndex,T}()
             for line in split(ret, "\n")
                 m_var = match(r"(.+) \= (.+)\;", line)
                 if m_var === nothing
+                    if !isempty(primal_solution)
+                        # We found a line in the output that is not a variable
+                        # statement. It must divide the solutions, so append
+                        # the current.
+                        push!(dest.primal_solutions, copy(primal_solution))
+                        empty!(primal_solution)
+                    end
                     continue
                 elseif m_var[1] == "_objective"
                     dest.primal_objective = _parse_result(T, m_var[2])
                 else
                     x = variable_map[m_var[1]]
-                    dest.primal_solution[x] = _parse_result(T, m_var[2])
+                    primal_solution[x] = _parse_result(T, m_var[2])
                 end
             end
         end
@@ -209,7 +222,7 @@ end
 
 function _has_solution(model::Optimizer)
     return model.solver_status == "SATISFIABLE" &&
-           !isempty(model.primal_solution)
+           !isempty(model.primal_solutions)
 end
 
 MOI.get(model::Optimizer, ::MOI.RawStatusString) = model.solver_status
@@ -218,7 +231,11 @@ function MOI.get(model::Optimizer, ::MOI.TerminationStatus)
     if model.solver_status == "UNSATISFIABLE"
         return MOI.INFEASIBLE
     elseif _has_solution(model)
-        return MOI.OPTIMAL
+        if 1 < model.options["num_solutions"] <= length(model.primal_solutions)
+            return MOI.SOLUTION_LIMIT
+        else
+            return MOI.OPTIMAL
+        end
     else
         return MOI.OTHER_ERROR
     end
@@ -234,9 +251,7 @@ end
 
 MOI.get(::Optimizer, ::MOI.DualStatus) = MOI.NO_SOLUTION
 
-function MOI.get(model::Optimizer, ::MOI.ResultCount)
-    return _has_solution(model) ? 1 : 0
-end
+MOI.get(model::Optimizer, ::MOI.ResultCount) = length(model.primal_solutions)
 
 function MOI.get(model::Optimizer, attr::MOI.ObjectiveValue)
     MOI.check_result_index_bounds(model, attr)
@@ -250,7 +265,7 @@ function MOI.get(
 )
     MOI.check_result_index_bounds(model, attr)
     MOI.throw_if_not_valid(model, x)
-    return model.primal_solution[x]
+    return model.primal_solutions[attr.result_index][x]
 end
 
 MOI.get(model::Optimizer, ::MOI.SolveTimeSec) = model.solve_time_sec

test/examples/nqueens_solveall.jl

@@ -0,0 +1,82 @@
+# Copyright (c) 2022 MiniZinc.jl contributors
+#
+# Use of this source code is governed by an MIT-style license that can be found
+# in the LICENSE.md file or at https://opensource.org/licenses/MIT.
+
+function _init_nqueens_solve_num_solutions()
+    n = 8
+    model = MOI.instantiate(
+        () -> MiniZinc.Optimizer{Int}("chuffed");
+        with_cache_type = Int,
+        with_bridge_type = Int,
+    )
+    MOI.set(model, MOI.RawOptimizerAttribute("model_filename"), "test.mzn")
+    q = MOI.add_variables(model, n)
+    MOI.add_constraint.(model, q, MOI.Interval(1, n))
+    MOI.add_constraint(model, MOI.VectorOfVariables(q), MOI.AllDifferent(n))
+    for op in (+, -)
+        f = MOI.Utilities.vectorize([op(q[i], i) for i in eachindex(q)])
+        MOI.add_constraint(model, f, MOI.AllDifferent(n))
+    end
+    return model, q
+end
+
+function _test_nqueens_solve_num_solutions(
+    model,
+    q,
+    actual_count = 92,
+    termination_status = MOI.OPTIMAL,
+)
+    n = 8
+    MOI.optimize!(model)
+    @test MOI.get(model, MOI.TerminationStatus()) === termination_status
+    res_count = MOI.get(model, MOI.ResultCount())
+    @test res_count == actual_count
+    for i in 1:res_count
+        q_sol = MOI.get(model, MOI.VariablePrimal(i), q)
+        @test allunique(q_sol)
+        @test allunique(q_sol .+ (1:n))
+        @test allunique(q_sol .- (1:n))
+    end
+    @test MOI.get(model, MOI.SolveTimeSec()) < 4.0
+    rm("test.mzn")
+    return
+end
+
+function test_nqueens_solve_num_solutions_100()
+    model, q = _init_nqueens_solve_num_solutions()
+    MOI.set(model, MOI.RawOptimizerAttribute("num_solutions"), 100)
+    _test_nqueens_solve_num_solutions(model, q)
+    return
+end
+
+function test_nqueens_solve_num_solutions_25()
+    model, q = _init_nqueens_solve_num_solutions()
+    MOI.set(model, MOI.RawOptimizerAttribute("num_solutions"), 25)
+    _test_nqueens_solve_num_solutions(model, q, 25, MOI.SOLUTION_LIMIT)
+    return
+end
+
+function test_nqueens_solve_num_solutions_not_set()
+    model, q = _init_nqueens_solve_num_solutions()
+    _test_nqueens_solve_num_solutions(model, q, 1)
+    return
+end
+
+function test_nqueens_solve_num_solutions_1()
+    model, q = _init_nqueens_solve_num_solutions()
+    MOI.set(model, MOI.RawOptimizerAttribute("num_solutions"), 1)
+    _test_nqueens_solve_num_solutions(model, q, 1)
+    return
+end
+
+function test_nqueens_num_solutions_throw()
+    model, _ = _init_nqueens_solve_num_solutions()
+    for value in (-1, 0, 1.1, "two")
+        @test_throws(
+            MOI.SetAttributeNotAllowed,
+            MOI.set(model, MOI.RawOptimizerAttribute("num_solutions"), -1),
+        )
+    end
+    return
+end