Add option to only use multiple-bigm on bound constraints, normal bigm on everything else

pyomo/gdp/plugins/bigm.py

@@ -368,6 +368,12 @@ def _transform_disjunct(self, obj, bigM, root_disjunct):
         # information for both.)
         relaxationBlock.bigm_src = {}
         relaxationBlock.localVarReferences = Block()
+        # add the map that will link back and forth between transformed
+        # constraints and their originals.
+        relaxationBlock._constraintMap = {
+            'srcConstraints': ComponentMap(),
+            'transformedConstraints': ComponentMap()
+        }
         relaxationBlock.transformedConstraints = Constraint(Any)
         obj._transformation_block = weakref_ref(relaxationBlock)
         relaxationBlock._src_disjunct = weakref_ref(obj)
@@ -438,19 +444,12 @@ def _warn_for_active_disjunct(self, innerdisjunct, outerdisjunct, bigMargs,
                                   arg_list, suffix_list):
         _warn_for_active_disjunct(innerdisjunct, outerdisjunct)
 
-    def _get_constraint_map_dict(self, transBlock):
-        if not hasattr(transBlock, "_constraintMap"):
-            transBlock._constraintMap = {
-                'srcConstraints': ComponentMap(),
-                'transformedConstraints': ComponentMap()}
-        return transBlock._constraintMap
-
     def _transform_constraint(self, obj, disjunct, bigMargs, arg_list,
                               disjunct_suffix_list):
         # add constraint to the transformation block, we'll transform it there.
         transBlock = disjunct._transformation_block()
         bigm_src = transBlock.bigm_src
-        constraintMap = self._get_constraint_map_dict(transBlock)
+        constraintMap = transBlock._constraintMap
 
         disjunctionRelaxationBlock = transBlock.parent_block()
 
@@ -459,18 +458,9 @@ def _transform_constraint(self, obj, disjunct, bigMargs, arg_list,
         # products is kind of expensive (and redundant since we have the
         # original model)
         newConstraint = transBlock.transformedConstraints
-        # Since we are both combining components from multiple blocks and using
-        # local names, we need to make sure that the first index for
-        # transformedConstraints is guaranteed to be unique. We just grab the
-        # current length of the list here since that will be monotonically
-        # increasing and hence unique. We'll append it to the
-        # slightly-more-human-readable constraint name for something familiar
-        # but unique.
-        unique = len(newConstraint)
 
         for i in sorted(obj.keys()):
             c = obj[i]
-            name = c.local_name + "_%s" % unique
             if not c.active:
                 continue
 
@@ -521,37 +511,54 @@ def _transform_constraint(self, obj, disjunct, bigMargs, arg_list,
             # save the source information
             bigm_src[c] = (lower, upper)
 
-            if c.lower is not None:
-                if M[0] is None:
-                    raise GDP_Error("Cannot relax disjunctive constraint '%s' "
-                                    "because M is not defined." % name)
-                M_expr = M[0] * (1 - disjunct.binary_indicator_var)
-                newConstraint.add((name, i, 'lb'), c.lower <= c. body - M_expr)
-                constraintMap[
-                    'transformedConstraints'][c] = [
-                        newConstraint[name, i, 'lb']]
-                constraintMap['srcConstraints'][
-                    newConstraint[name, i, 'lb']] = c
-            if c.upper is not None:
-                if M[1] is None:
-                    raise GDP_Error("Cannot relax disjunctive constraint '%s' "
-                                    "because M is not defined." % name)
-                M_expr = M[1] * (1 - disjunct.binary_indicator_var)
-                newConstraint.add((name, i, 'ub'), c.body - M_expr <= c.upper)
-                transformed = constraintMap['transformedConstraints'].get(c)
-                if transformed is not None:
-                    constraintMap['transformedConstraints'][
-                        c].append(newConstraint[name, i, 'ub'])
-                else:
-                    constraintMap[
-                        'transformedConstraints'][c] = [
-                            newConstraint[name, i, 'ub']]
-                constraintMap['srcConstraints'][
-                    newConstraint[name, i, 'ub']] = c
+            self._add_constraint_expressions(c, i, M,
+                                             disjunct.binary_indicator_var,
+                                             newConstraint, constraintMap)
 
             # deactivate because we relaxed
             c.deactivate()
 
+    def _add_constraint_expressions(self, c, i, M, indicator_var, newConstraint,
+                                    constraintMap):
+        # Since we are both combining components from multiple blocks and using
+        # local names, we need to make sure that the first index for
+        # transformedConstraints is guaranteed to be unique. We just grab the
+        # current length of the list here since that will be monotonically
+        # increasing and hence unique. We'll append it to the
+        # slightly-more-human-readable constraint name for something familiar
+        # but unique. (Note that we really could do this outside of the loop
+        # over the constraint indices, but I don't think it matters a lot.)
+        unique = len(newConstraint)
+        name = c.local_name + "_%s" % unique
+
+        if c.lower is not None:
+            if M[0] is None:
+                raise GDP_Error("Cannot relax disjunctive constraint '%s' "
+                                "because M is not defined." % name)
+            M_expr = M[0] * (1 - indicator_var)
+            newConstraint.add((name, i, 'lb'), c.lower <= c. body - M_expr)
+            constraintMap[
+                'transformedConstraints'][c] = [
+                    newConstraint[name, i, 'lb']]
+            constraintMap['srcConstraints'][
+                newConstraint[name, i, 'lb']] = c
+        if c.upper is not None:
+            if M[1] is None:
+                raise GDP_Error("Cannot relax disjunctive constraint '%s' "
+                                "because M is not defined." % name)
+            M_expr = M[1] * (1 - indicator_var)
+            newConstraint.add((name, i, 'ub'), c.body - M_expr <= c.upper)
+            transformed = constraintMap['transformedConstraints'].get(c)
+            if transformed is not None:
+                constraintMap['transformedConstraints'][
+                    c].append(newConstraint[name, i, 'ub'])
+            else:
+                constraintMap[
+                    'transformedConstraints'][c] = [
+                        newConstraint[name, i, 'ub']]
+            constraintMap['srcConstraints'][
+                newConstraint[name, i, 'ub']] = c
+
     def _process_M_value(self, m, lower, upper, need_lower, need_upper, src,
                          key, constraint, from_args=False):
         m = _convert_M_to_tuple(m, constraint)

pyomo/gdp/plugins/multiple_bigm.py

@@ -18,7 +18,7 @@
 from pyomo.common.modeling import unique_component_name
 
 from pyomo.core import (
-    Binary, Block, BooleanVar, Connector, Constraint, Expression,
+    Any, Binary, Block, BooleanVar, Connector, Constraint, Expression,
     ExternalFunction, maximize, minimize, NonNegativeIntegers, Objective,
     Param, RangeSet, Set, SetOf, SortComponents, Suffix, value, Var
 )
@@ -105,7 +105,9 @@ class MultipleBigMTransformation(Transformation):
 
         Note: Unlike in the bigm transformation, we require the keys in this
         mapping specify the components the M value applies to exactly in order
-        to avoid ambiguity.
+        to avoid ambiguity. However, if the 'only_mbigm_bound_constraints'
+        option is True, this argument can be used as it would be in the
+        traditional bigm transformation for the non-bound constraints.
         """
     ))
     CONFIG.declare('reduce_bound_constraints', ConfigValue(
@@ -140,6 +142,25 @@ class MultipleBigMTransformation(Transformation):
             Techniques," SIAM Review, vol. 57, no. 1, 2015, pp. 3-57.
         """
     ))
+    CONFIG.declare('only_mbigm_bound_constraints', ConfigValue(
+        default=False,
+        domain=bool,
+        description="Flag indicating if only bound constraints should be "
+        "transformed with multiple-bigm, or if all the disjunctive "
+        "constraints should.",
+        doc="""
+        Sometimes it is only computationally advantageous to apply multiple-
+        bigm to disjunctive constraints with the special structure:
+
+        [l_1 <= x <= u_1] v [l_2 <= x <= u_2] v ... v [l_K <= x <= u_K],
+
+        and transform other disjunctive constraints with the traditional
+        big-M transformation. This flag is used to set the above behavior.
+
+        Note that the reduce_bound_constraints flag must also be True when
+        this flag is set to True.
+        """
+    ))
 
     def __init__(self):
         super(MultipleBigMTransformation, self).__init__()
@@ -171,6 +192,7 @@ def __init__(self):
         }
         self._transformation_blocks = {}
         self._algebraic_constraints = {}
+        self._arg_list = {}
 
     def _apply_to(self, instance, **kwds):
         self.used_args = ComponentMap()
@@ -180,6 +202,7 @@ def _apply_to(self, instance, **kwds):
             self.used_args.clear()
             self._transformation_blocks.clear()
             self._algebraic_constraints.clear()
+            self._arg_list.clear()
 
     def _apply_to_impl(self, instance, **kwds):
         if not instance.ctype in (Block, Disjunct):
@@ -191,6 +214,15 @@ def _apply_to_impl(self, instance, **kwds):
         self._config = self.CONFIG(kwds.pop('options', {}))
         self._config.set_value(kwds)
 
+        if (self._config.only_mbigm_bound_constraints and not
+            self._config.reduce_bound_constraints):
+            raise GDP_Error("The 'only_mbigm_bound_constraints' option is set "
+                            "to True, but the 'reduce_bound_constraints' "
+                            "option is not. This is not supported--please also "
+                            "set 'reduce_bound_constraints' to True if you "
+                            "only wish to transform the bound constraints with "
+                            "multiple bigm.")
+
         targets = self._config.targets
         knownBlocks = {}
         if targets is None:
@@ -272,9 +304,12 @@ def _transform_disjunctionData(self, obj, index, parent_disjunct,
             transformed_constraints = self._transform_bound_constraints(
                 active_disjuncts, transBlock, arg_Ms)
 
-        Ms = transBlock.calculated_missing_m_values = self.\
-             _calculate_missing_M_values(active_disjuncts, arg_Ms, transBlock,
-                                         transformed_constraints)
+        Ms = arg_Ms
+        if not self._config.only_mbigm_bound_constraints:
+            Ms = transBlock.calculated_missing_m_values = self.\
+                 _calculate_missing_M_values(active_disjuncts, arg_Ms,
+                                             transBlock,
+                                             transformed_constraints)
 
         # Now we can deactivate the constraints we deferred, so that we don't
         # re-transform them
@@ -396,31 +431,63 @@ def _transform_constraint(self, obj, disjunct, active_disjuncts, Ms):
         name = unique_component_name(relaxationBlock, obj.getname(
             fully_qualified=False))
 
-        newConstraint = Constraint(obj.index_set(), transBlock.lbub)
+        newConstraint = Constraint(Any)
         relaxationBlock.add_component(name, newConstraint)
+        bigm = TransformationFactory('gdp.bigm')
+        bigm.assume_fixed_vars_permanent = self._config.\
+                                           assume_fixed_vars_permanent
+        bigm.used_args = self.used_args
 
         for i in sorted(obj.keys()):
             c = obj[i]
             if not c.active:
                 continue
 
-            transformed = []
-            if c.lower is not None:
-                rhs = sum(Ms[c,
-                             disj][0]*disj.indicator_var.get_associated_binary()
-                          for disj in active_disjuncts if disj is not disjunct)
-                newConstraint.add((i, 'lb'), c.body - c.lower >= rhs)
-                transformed.append(newConstraint[i, 'lb'])
-
-            if c.upper is not None:
-                rhs = sum(Ms[c,
-                             disj][1]*disj.indicator_var.get_associated_binary()
-                          for disj in active_disjuncts if disj is not disjunct)
-                newConstraint.add((i, 'ub'), c.body - c.upper <= rhs)
-                transformed.append(newConstraint[i, 'ub'])
-            for c_new in transformed:
-                constraintMap['srcConstraints'][c_new] = [c]
-            constraintMap['transformedConstraints'][c] = transformed
+            if not self._config.only_mbigm_bound_constraints:
+                transformed = []
+                if c.lower is not None:
+                    rhs = sum(
+                        Ms[c,
+                           disj][0]*disj.indicator_var.get_associated_binary()
+                        for disj in active_disjuncts if disj is not disjunct)
+                    newConstraint.add((i, 'lb'), c.body - c.lower >= rhs)
+                    transformed.append(newConstraint[i, 'lb'])
+
+                if c.upper is not None:
+                    rhs = sum(
+                        Ms[c,
+                           disj][1]*disj.indicator_var.get_associated_binary()
+                        for disj in active_disjuncts if disj is not disjunct)
+                    newConstraint.add((i, 'ub'), c.body - c.upper <= rhs)
+                    transformed.append(newConstraint[i, 'ub'])
+                for c_new in transformed:
+                    constraintMap['srcConstraints'][c_new] = [c]
+                constraintMap['transformedConstraints'][c] = transformed
+            else:
+                lower = (None, None, None)
+                upper = (None, None, None)
+
+                if disjunct not in self._arg_list:
+                    self._arg_list[disjunct] = bigm._get_bigm_arg_list(
+                        self._config.bigM, disjunct)
+                arg_list = self._arg_list[disjunct]
+
+                # first, we see if an M value was specified in the arguments.
+                # (This returns None if not)
+                lower, upper = bigm._get_M_from_args(c, Ms, arg_list, lower,
+                                                     upper)
+                M = (lower[0], upper[0])
+
+                # estimate if we don't have what we need
+                if c.lower is not None and M[0] is None:
+                    M = (bigm._estimate_M(c.body, c)[0] - c.lower, M[1])
+                    lower = (M[0], None, None)
+                if c.upper is not None and M[1] is None:
+                    M = (M[0], bigm._estimate_M(c.body, c)[1] - c.upper)
+                    upper = (M[1], None, None)
+                bigm._add_constraint_expressions(
+                    c, i, M, disjunct.indicator_var.get_associated_binary(),
+                    newConstraint, constraintMap)
 
         # deactivate now that we have transformed
         c.deactivate()
@@ -549,7 +616,7 @@ def _add_transformation_block(self, block):
         # transformed components
         transBlockName = unique_component_name(
             block,
-            '_pyomo_gdp_hull_reformulation')
+            '_pyomo_gdp_mbigm_reformulation')
         transBlock = Block()
         block.add_component(transBlockName, transBlock)
         self._transformation_blocks[block] = transBlock