[FileFormats.LP] fix reading file with free variable and explicit bou…

…nds (#2225)

src/FileFormats/LP/LP.jl

@@ -298,15 +298,6 @@ function _write_constraints(io, model, S, variable_names)
     return
 end
 
-function _write_bounds(io, model, S, variable_names, free_variables)
-    F = MOI.VariableIndex
-    for index in MOI.get(model, MOI.ListOfConstraintIndices{F,S}())
-        delete!(free_variables, MOI.VariableIndex(index.value))
-        _write_constraint(io, model, index, variable_names; write_name = false)
-    end
-    return
-end
-
 function _write_sos_constraints(io, model, variable_names)
     T, F = Float64, MOI.VectorOfVariables
     sos1_indices = MOI.get(model, MOI.ListOfConstraintIndices{F,MOI.SOS1{T}}())
@@ -375,19 +366,31 @@ function Base.write(io::IO, model::Model)
         _write_constraints(io, model, S, variable_names)
     end
     println(io, "Bounds")
-    for S in _SCALAR_SETS
-        _write_bounds(io, model, S, variable_names, free_variables)
-    end
-    # If a variable is binary, it should not be listed as `free` in the bounds
-    # section.
-    attr = MOI.ListOfConstraintIndices{MOI.VariableIndex,MOI.ZeroOne}()
-    for index in MOI.get(model, attr)
-        delete!(free_variables, MOI.VariableIndex(index.value))
-    end
-    # By default, variables have bounds of [0, ∞), so we need to explicitly
-    # declare variables as free.
-    for variable in sort(collect(free_variables), by = x -> x.value)
-        println(io, variable_names[variable], " free")
+    CI = MOI.ConstraintIndex{MOI.VariableIndex,MOI.ZeroOne}
+    for x in MOI.get(model, MOI.ListOfVariableIndices())
+        lb, ub = MOI.Utilities.get_bounds(model, Float64, x)
+        if lb == -Inf && ub == Inf
+            if MOI.is_valid(model, CI(x.value))
+                # If a variable is binary, it should not be listed as `free` in
+                # the bounds section.
+                continue
+            end
+            print(io, variable_names[x], " free")
+        elseif lb == ub
+            print(io, variable_names[x], " = ")
+            _print_shortest(io, lb)
+        elseif lb == -Inf
+            print(io, "-infinity <= ", variable_names[x], " <= ")
+            _print_shortest(io, ub)
+        elseif ub == Inf
+            print(io, variable_names[x], " >= ")
+            _print_shortest(io, lb)
+        else
+            _print_shortest(io, lb)
+            print(io, " <= ", variable_names[x], " <= ")
+            _print_shortest(io, ub)
+        end
+        println(io)
     end
     _write_integrality(io, model, "General", MOI.Integer, variable_names)
     _write_integrality(io, model, "Binary", MOI.ZeroOne, variable_names)
@@ -759,7 +762,7 @@ function _parse_section(
         _delete_default_lower_bound_if_present(model, cache, x)
         return
     end
-    lb, ub, name = -Inf, Inf, ""
+    lb, ub, name = nothing, nothing, ""
     if length(tokens) == 5
         name = tokens[3]
         if _is_less_than(tokens[2]) && _is_less_than(tokens[4])
@@ -810,16 +813,27 @@ function _parse_section(
         error("Unable to parse bound: $(line)")
     end
     x = _get_variable_from_name(model, cache, name)
-    if lb == ub
-        _delete_default_lower_bound_if_present(model, cache, x)
-        MOI.add_constraint(model, x, MOI.EqualTo(lb))
-    elseif -Inf < lb < ub < Inf
-        _delete_default_lower_bound_if_present(model, cache, x)
-        MOI.add_constraint(model, x, MOI.Interval(lb, ub))
-    elseif -Inf < lb
+    if lb !== nothing && ub !== nothing
+        if lb == ub
+            _delete_default_lower_bound_if_present(model, cache, x)
+            MOI.add_constraint(model, x, MOI.EqualTo(lb))
+            return
+        elseif -Inf < lb < ub < Inf
+            _delete_default_lower_bound_if_present(model, cache, x)
+            MOI.add_constraint(model, x, MOI.Interval(lb, ub))
+            return
+        elseif lb == -Inf
+            _delete_default_lower_bound_if_present(model, cache, x)
+            if ub == Inf
+                return  # Explicitly free variable
+            end
+        end
+    end
+    if lb !== nothing && -Inf < lb
         _delete_default_lower_bound_if_present(model, cache, x)
         MOI.add_constraint(model, x, MOI.GreaterThan(lb))
-    else
+    end
+    if ub !== nothing && ub < Inf
         if ub < 0
             # We only need to delete the default lower bound if the upper bound
             # is less than 0.

test/FileFormats/LP/LP.jl

@@ -48,11 +48,10 @@ c12: [x, y, z] in SOS2{Float64}([3.3, 1.1, 2.2])
           "c7: 1.6 + 1.5 a = 0.2\n" *
           "c8: 0.3 <= 1.8 + 1.7 a <= 0.4\n" *
           "Bounds\n" *
-          "x <= 2\n" *
-          "x >= -1\n" *
+          "a free\n" *
+          "-1 <= x <= 2\n" *
           "y = 3\n" *
           "4 <= z <= 5\n" *
-          "a free\n" *
           "General\n" *
           "y\n" *
           "Binary\n" *
@@ -465,15 +464,14 @@ function test_read_model1_tricky()
     @test occursin("CON1: 1 V1 >= 0", file)
     @test occursin("CON5: [ 1 Var4 ^ 2 - 1.2 V5 * V1 ] <= 0", file)
     @test occursin("R1: 1 V2 >= 2", file)
-    @test occursin("V1 <= 3", file)
+    @test occursin("-infinity <= V1 <= 3", file)
     @test occursin("Var4 >= 5.5", file)
     @test occursin("V3 >= -3", file)
     @test occursin("V5 = 1", file)
-    @test occursin("V2 <= 3", file)
-    @test occursin("V2 >= 0", file)
+    @test occursin("0 <= V2 <= 3", file)
+    @test occursin("V6 free", file)
     @test occursin("0 <= V7 <= 1", file)
     @test occursin("0 <= V8 <= 1", file)
-    @test occursin("V6 free", file)
     @test occursin("\nVar4\n", file)
     @test occursin("\nV5\n", file)
     @test occursin("\nV6\n", file)
@@ -718,15 +716,15 @@ end
 function test_wrong_way_bounds()
     for (case, result) in [
         "x >= 2" => "x >= 2",
-        "x <= 2" => "x <= 2\nx >= 0",
+        "x <= 2" => "0 <= x <= 2",
         "x == 2" => "x = 2",
         "x > 2" => "x >= 2",
-        "x < 2" => "x <= 2\nx >= 0",
+        "x < 2" => "0 <= x <= 2",
         "x = 2" => "x = 2",
-        "2 >= x" => "x <= 2\nx >= 0",
+        "2 >= x" => "0 <= x <= 2",
         "2 <= x" => "x >= 2",
         "2 == x" => "x = 2",
-        "2 > x" => "x <= 2\nx >= 0",
+        "2 > x" => "0 <= x <= 2",
         "2 < x" => "x >= 2",
         "2 = x" => "x = 2",
     ]
@@ -789,19 +787,19 @@ function test_reading_bounds()
     _test_round_trip("0 < x", "Bounds\nx >= 0\nEnd")
     _test_round_trip("-1 < x", "Bounds\nx >= -1\nEnd")
     # Test upper bound
-    _test_round_trip("x <= 1", "Bounds\nx <= 1\nx >= 0\nEnd")
-    _test_round_trip("x <= 0", "Bounds\nx <= 0\nx >= 0\nEnd")
-    _test_round_trip("x <= -1", "Bounds\nx <= -1\nEnd")
-    _test_round_trip("x < 1", "Bounds\nx <= 1\nx >= 0\nEnd")
-    _test_round_trip("x < 0", "Bounds\nx <= 0\nx >= 0\nEnd")
-    _test_round_trip("x < -1", "Bounds\nx <= -1\nEnd")
+    _test_round_trip("x <= 1", "Bounds\n0 <= x <= 1\nEnd")
+    _test_round_trip("x <= 0", "Bounds\nx = 0\nEnd")
+    _test_round_trip("x <= -1", "Bounds\n-infinity <= x <= -1\nEnd")
+    _test_round_trip("x < 1", "Bounds\n0 <= x <= 1\nEnd")
+    _test_round_trip("x < 0", "Bounds\nx = 0\nEnd")
+    _test_round_trip("x < -1", "Bounds\n-infinity <= x <= -1\nEnd")
     # Test reversed upper bound
-    _test_round_trip("1 >= x", "Bounds\nx <= 1\nx >= 0\nEnd")
-    _test_round_trip("0 >= x", "Bounds\nx <= 0\nx >= 0\nEnd")
-    _test_round_trip("-1 >= x", "Bounds\nx <= -1\nEnd")
-    _test_round_trip("1 > x", "Bounds\nx <= 1\nx >= 0\nEnd")
-    _test_round_trip("0 > x", "Bounds\nx <= 0\nx >= 0\nEnd")
-    _test_round_trip("-1 > x", "Bounds\nx <= -1\nEnd")
+    _test_round_trip("1 >= x", "Bounds\n0 <= x <= 1\nEnd")
+    _test_round_trip("0 >= x", "Bounds\nx = 0\nEnd")
+    _test_round_trip("-1 >= x", "Bounds\n-infinity <= x <= -1\nEnd")
+    _test_round_trip("1 > x", "Bounds\n0 <= x <= 1\nEnd")
+    _test_round_trip("0 > x", "Bounds\nx = 0\nEnd")
+    _test_round_trip("-1 > x", "Bounds\n-infinity <= x <= -1\nEnd")
     # Test equality
     _test_round_trip("x == 1", "Bounds\nx = 1\nEnd")
     _test_round_trip("x == 0", "Bounds\nx = 0\nEnd")
@@ -822,13 +820,13 @@ function test_reading_bounds()
     _test_round_trip("0 <= x <= 0", "Bounds\nx = 0\nEnd")
     _test_round_trip("-2 <= x <= -2", "Bounds\nx = -2\nEnd")
     # Test upper then lower
-    _test_round_trip("x <= 1\nx >= 0", "Bounds\nx <= 1\nx >= 0\nEnd")
-    _test_round_trip("x <= 2\nx >= 1", "Bounds\nx <= 2\nx >= 1\nEnd")
-    _test_round_trip("x <= 2\nx >= -1", "Bounds\nx <= 2\nx >= -1\nEnd")
+    _test_round_trip("x <= 1\nx >= 0", "Bounds\n0 <= x <= 1\nEnd")
+    _test_round_trip("x <= 2\nx >= 1", "Bounds\n1 <= x <= 2\nEnd")
+    _test_round_trip("x <= 2\nx >= -1", "Bounds\n-1 <= x <= 2\nEnd")
     # Test lower then upper
-    _test_round_trip("x >= 0\nx <= 1", "Bounds\nx <= 1\nx >= 0\nEnd")
-    _test_round_trip("x >= 1\nx <= 2", "Bounds\nx <= 2\nx >= 1\nEnd")
-    _test_round_trip("x >= -1\nx <= 2", "Bounds\nx <= 2\nx >= -1\nEnd")
+    _test_round_trip("x >= 0\nx <= 1", "Bounds\n0 <= x <= 1\nEnd")
+    _test_round_trip("x >= 1\nx <= 2", "Bounds\n1 <= x <= 2\nEnd")
+    _test_round_trip("x >= -1\nx <= 2", "Bounds\n-1 <= x <= 2\nEnd")
     return
 end
 
@@ -942,6 +940,43 @@ function test_read_newline_breaks()
     return
 end
 
+function test_read_variable_bounds()
+    io = IOBuffer("""
+    maximize
+    obj: 1 x1
+    subject to
+    bounds
+    -infinity <= x1 <= +infinity
+    -infinity <= x2 <= 1
+    -infinity <= x3 <= -1
+    -1 <= x4 <= +infinity
+    1 <= x5 <= +infinity
+    -1 <= x6 <= 1
+    1 <= x7 <= 1
+    end
+    """)
+    model = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_LP)
+    read!(io, model)
+    io = IOBuffer()
+    write(io, model)
+    seekstart(io)
+    @test read(io, String) == """
+    maximize
+    obj: 1 x1
+    subject to
+    Bounds
+    x1 free
+    -infinity <= x2 <= 1
+    -infinity <= x3 <= -1
+    x4 >= -1
+    x5 >= 1
+    -1 <= x6 <= 1
+    x7 = 1
+    End
+    """
+    return
+end
+
 function runtests()
     for name in names(@__MODULE__, all = true)
         if startswith("$(name)", "test_")