Corrected handling of solution_loader. Implemented bounded constraint and writing to gms.

Author: Norman_Tran

pyomo/contrib/solver/solvers/gams.py

@@ -594,7 +594,13 @@ def solve(self, model, **kwds):
                 results.gams_termination_condition
             ]
             obj = list(model.component_data_objects(Objective, active=True))
-            assert len(obj) == 1, 'Only one objective is allowed.'
+
+            # NOTE: How should gams handle when no objective is provided
+            # NOTE: pyomo/contrib/solver/tests/solvers/test_solvers.py::TestSolvers::test_no_objective
+            # NOTE: results.incumbent_objective = None
+            # NOTE: results.objective_bound = None
+            # assert len(obj) == 1, 'Only one objective is allowed.'
+
             if results.solution_status in {
                 SolutionStatus.feasible,
                 SolutionStatus.optimal,
@@ -605,7 +611,10 @@ def solve(self, model, **kwds):
 
                 if config.load_solutions:
                     results.solution_loader.load_vars()
-                    results.incumbent_objective = stat_vars["OBJVAL"]
+                    if len(obj) == 1:
+                        results.incumbent_objective = stat_vars["OBJVAL"]
+                    else:
+                        results.incumbent_objective = None
                     if (
                         hasattr(model, 'dual')
                         and isinstance(model.dual, Suffix)

pyomo/contrib/solver/solvers/gms_sol_reader.py

@@ -81,8 +81,11 @@ def get_primals(
         if vars_to_load is None:
             vars_to_load = self._gms_info.var_symbol_map.bySymbol.items()
 
-        for sym, obj in vars_to_load:
-            res[obj] = val_map[id(obj)]
+            for sym, obj in vars_to_load:
+                res[obj] = val_map[id(obj)]
+        else:
+            for obj in vars_to_load:
+                res[obj] = val_map[id(obj)]
 
         return res
 
@@ -100,14 +103,22 @@ def get_duals(
                 'check results.termination_condition and/or results.solution_status.'
             )
 
-        res = ComponentMap()
+        con_map = {}
+        if self._gdx_data is None:
+            assert len(self._gms_info.con_symbol_map.bySymbol) == 0
+        else:
+            for sym, obj in self._gms_info.con_symbol_map.bySymbol.items():
+                con_map[id(obj)] = self._gdx_data[sym][1]
 
+        res = ComponentMap()
         if cons_to_load is None:
-            cons_to_load = set(self._gms_info.con_symbol_map.bySymbol.keys())
+            cons_to_load = self._gms_info.con_symbol_map.bySymbol.items()
 
-        for sym, con in self._gms_info.con_symbol_map.bySymbol.items():
-            if sym in cons_to_load and con.parent_component().ctype is not Objective:
-                res[con] = self._gdx_data[sym][1]
+            for sym, obj in cons_to_load:
+                res[obj] = con_map[id(obj)]
+        else:
+            for obj in cons_to_load:
+                res[obj] = con_map[id(obj)]
 
         return res
 
@@ -123,11 +134,21 @@ def get_reduced_costs(self, vars_to_load=None):
                 'check results.termination_condition and/or results.solution_status.'
             )
 
+        var_map = {}
+        if self._gdx_data is None:
+            assert len(self._gms_info.var_symbol_map.bySymbol) == 0
+        else:
+            for sym, obj in self._gms_info.var_symbol_map.bySymbol.items():
+                var_map[id(obj)] = self._gdx_data[sym][1]
+
         res = ComponentMap()
         if vars_to_load is None:
             vars_to_load = self._gms_info.var_symbol_map.bySymbol.items()
 
-        for sym, obj in vars_to_load:
-            res[obj] = self._gdx_data[sym][1]
+            for sym, obj in vars_to_load:
+                res[obj] = var_map[id(obj)]
+        else:
+            for obj in vars_to_load:
+                res[obj] = var_map[id(obj)]
 
         return res

pyomo/repn/plugins/gams_writer_v2.py

@@ -30,26 +30,21 @@
     Param,
     Expression,
     SOSConstraint,
-    SortComponents,
     Suffix,
     SymbolMap,
     minimize,
     ShortNameLabeler,
 )
-from pyomo.core.base.component import ActiveComponent
 from pyomo.core.base.label import NumericLabeler
 from pyomo.opt import WriterFactory
 from pyomo.repn.util import ftoa
 
-# from pyomo.repn.quadratic import QuadraticRepnVisitor
 from pyomo.repn.linear import LinearRepnVisitor
 from pyomo.repn.util import (
     FileDeterminism,
     FileDeterminism_to_SortComponents,
     OrderedVarRecorder,
     categorize_valid_components,
-    initialize_var_map_from_column_order,
-    int_float,
     ordered_active_constraints,
 )
 
@@ -444,7 +439,6 @@ def write(self, model):
 
             con_symbol = con_labeler(con)
             declaration, definition, bounds = None, None, None
-
             if lb is not None:
                 if ub is None:
                     label = f'{con_symbol}_lo'
@@ -463,10 +457,23 @@ def write(self, model):
                     bounds = f' =E= {(lb - offset)!s};'
                     con_list[label] = declaration + definition + bounds
                 else:
-                    raise NotImplementedError(
-                        "Bounded constraints within the same expression is not supported"
-                    )
-
+                    # We will need the constraint body twice.
+                    # Procedure is taken from lp_writer.py
+                    label = f'{con_symbol}_lo'
+                    self.con_symbol_map.addSymbol(con, label)
+                    self.var_symbol_map.addSymbol(con, label)
+                    declaration = f'\n{label}.. '
+                    definition = self.write_expression(ostream, repn)
+                    bounds = f' =G= {(lb - offset)!s};'
+                    con_list[label] = declaration + definition + bounds
+                    #
+                    label = f'{con_symbol}_hi'
+                    self.con_symbol_map.alias(con, label)
+                    self.var_symbol_map.alias(con, label)
+                    declaration = f'\n{label}.. '
+                    definition = self.write_expression(ostream, repn)
+                    bounds = f' =L= {(ub - offset)!s};'
+                    con_list[label] = declaration + definition + bounds
             elif ub is not None:
                 label = f'{con_symbol}_hi'
                 self.con_symbol_map.addSymbol(con, label)
@@ -549,14 +556,13 @@ def write(self, model):
         # Writing out the equations/constraints
         #
         ostream.write("EQUATIONS \n")
-        for id, cid in enumerate(self.con_symbol_map.byObject.keys()):
-            c = self.con_symbol_map.byObject[cid]
-            if id != len(self.con_symbol_map.byObject.keys()) - 1:
-                ostream.write(f"\t{c}\n")
+        for count, (sym, con) in enumerate(con_list.items()):
+            if count != len(con_list.keys()) - 1:
+                ostream.write(f"\t{sym}\n")
             else:
-                ostream.write(f"\t{c};\n\n")
+                ostream.write(f"\t{sym};\n\n")
 
-        for con_label, con in con_list.items():
+        for _, con in con_list.items():
             ostream.write(con)
 
         #