Adding public API to get the number of pieces in a piecewise linear f…

…unction

pyomo/contrib/piecewise/piecewise_linear_function.py

@@ -50,6 +50,15 @@ def __init__(self, component=None):
             self._points = []
             self._linear_functions = []
 
+    @property
+    def num_pieces(self):
+        """
+        Returns the number of domain-linear function pairs that define this piecewise-
+        linear function. Note that it is possible for contiguous domains to have the
+        same function, and in that case they will each be counted by this metric.
+        """
+        return len(self._linear_functions)
+
     def __call__(self, *args):
         """
         Returns a PiecewiseLinearExpression which is an instance of this

pyomo/contrib/piecewise/tests/test_piecewise_linear_function.py

@@ -75,6 +75,8 @@ def check_ln_x_approx(self, pw, x):
             places=7,
         )
 
+        self.assertEqual(pw.num_pieces, 3)
+
     def check_x_squared_approx(self, pw, x):
         self.assertEqual(len(pw._simplices), 3)
         self.assertEqual(len(pw._linear_functions), 3)
@@ -93,6 +95,8 @@ def check_x_squared_approx(self, pw, x):
             self, pw._linear_functions[2](x), 16 * x - 60, places=7
         )
 
+        self.assertEqual(pw.num_pieces, 3)
+
     def test_pw_linear_approx_of_ln_x_simplices(self):
         m = self.make_ln_x_model()
         simplices = [(1, 3), (3, 6), (6, 10)]