contrib.piecewise: Adding nonlinear-to-piecewise-linear transformation

.github/workflows/test_branches.yml

@@ -21,8 +21,8 @@ defaults:
 env:
   PYTHONWARNINGS: ignore::UserWarning
   PYTHON_CORE_PKGS: wheel
-  PYPI_ONLY: z3-solver
-  PYPY_EXCLUDE: scipy numdifftools seaborn statsmodels
+  PYPI_ONLY: z3-solver linear-tree
+  PYPY_EXCLUDE: scipy numdifftools seaborn statsmodels linear-tree
   CACHE_VER: v221013.1
   NEOS_EMAIL: tests@pyomo.org
   SRC_REF: ${{ github.head_ref || github.ref }}

.github/workflows/test_pr_and_main.yml

@@ -29,8 +29,8 @@ defaults:
 env:
   PYTHONWARNINGS: ignore::UserWarning
   PYTHON_CORE_PKGS: wheel
-  PYPI_ONLY: z3-solver
-  PYPY_EXCLUDE: scipy numdifftools seaborn statsmodels
+  PYPI_ONLY: z3-solver linear-tree
+  PYPY_EXCLUDE: scipy numdifftools seaborn statsmodels linear-tree
   CACHE_VER: v221013.1
   NEOS_EMAIL: tests@pyomo.org
   SRC_REF: ${{ github.head_ref || github.ref }}

pyomo/contrib/piecewise/__init__.py

@@ -33,6 +33,10 @@
 from pyomo.contrib.piecewise.transform.convex_combination import (
     ConvexCombinationTransformation,
 )
+from pyomo.contrib.piecewise.transform.nonlinear_to_pwl import (
+    DomainPartitioningMethod,
+    NonlinearToPWL,
+)
 from pyomo.contrib.piecewise.transform.nested_inner_repn import (
     NestedInnerRepresentationGDPTransformation,
 )

pyomo/contrib/piecewise/piecewise_linear_function.py

@@ -43,6 +43,10 @@
         BlockData.__init__(self, component)
 
         with self._declare_reserved_components():
+            # map of PiecewiseLinearExpression objects to integer indices in
+            # self._expressions
+            self._expression_ids = ComponentMap()
+            # index is monotonically increasing integer
             self._expressions = Expression(NonNegativeIntegers)
             self._transformed_exprs = ComponentMap()
             self._simplices = None
@@ -63,8 +67,9 @@
             return self._evaluate(*args)
         else:
             expr = PiecewiseLinearExpression(args, self)
-            idx = id(expr)
+            idx = len(self._expressions)
             self._expressions[idx] = expr
+            self._expression_ids[expr] = idx
             return self._expressions[idx]
 
     def _evaluate(self, *args):
@@ -134,7 +139,12 @@
         Records on the PiecewiseLinearFunction object that the transformed
         form of the PiecewiseLinearExpression object pw_expr is the Var v.
         """
-        self._transformed_exprs[self._expressions[id(pw_expr)]] = v
+        if pw_expr not in self._expression_ids:
+            raise DeveloperError(
+                "ID of PiecewiseLinearExpression '%s' not in the _expression_ids "
+                "dictionary of PiecewiseLinearFunction '%s'" % (pw_expr, self)
+            )
+        self._transformed_exprs[self._expressions[self._expression_ids[pw_expr]]] = v
 
     def get_transformation_var(self, pw_expr):
         """
@@ -159,7 +169,7 @@
 
 
 class _multivariate_linear_functor(AutoSlots.Mixin):
-    __slots__ = 'normal'
+    __slots__ = ('normal',)
 
     def __init__(self, normal):
         self.normal = normal