#961 fix interpolant ids

pybamm/expression_tree/interpolant.py

@@ -31,7 +31,13 @@ class Interpolant(pybamm.Function):
     """
 
     def __init__(
-        self, data, child, name=None, interpolator="cubic spline", extrapolate=True
+        self,
+        data,
+        child,
+        name=None,
+        interpolator="cubic spline",
+        extrapolate=True,
+        entries_string=None,
     ):
         if data.ndim != 2 or data.shape[1] != 2:
             raise ValueError(
@@ -56,22 +62,45 @@ def __init__(
             name = "interpolating function ({})".format(name)
         else:
             name = "interpolating function"
+        self.data = data
+        self.entries_string = entries_string
         super().__init__(
             interpolating_function, child, name=name, derivative="derivative"
         )
         # Store information as attributes
-        self.data = data
         self.x = data[:, 0]
         self.y = data[:, 1]
         self.interpolator = interpolator
         self.extrapolate = extrapolate
 
+    @property
+    def entries_string(self):
+        return self._entries_string
+
+    @entries_string.setter
+    def entries_string(self, value):
+        # We must include the entries in the hash, since different arrays can be
+        # indistinguishable by class, name and domain alone
+        # Slightly different syntax for sparse and non-sparse matrices
+        if value is not None:
+            self._entries_string = value
+        else:
+            entries = self.data
+            self._entries_string = entries.tostring()
+
+    def set_id(self):
+        """ See :meth:`pybamm.Symbol.set_id()`. """
+        self._id = hash(
+            (self.__class__, self.name, self.entries_string) + tuple(self.domain)
+        )
+
     def _function_new_copy(self, children):
         """ See :meth:`Function._function_new_copy()` """
         return pybamm.Interpolant(
             self.data,
             *children,
             name=self.name,
             interpolator=self.interpolator,
-            extrapolate=self.extrapolate
+            extrapolate=self.extrapolate,
+            entries_string=self.entries_string
         )

tests/unit/test_parameters/test_parameter_values.py

@@ -331,11 +331,11 @@ def test_process_interpolant(self):
         x = np.linspace(0, 10)[:, np.newaxis]
         data = np.hstack([x, 2 * x])
         parameter_values = pybamm.ParameterValues(
-            {"a": 3.01, "Diffusivity": ("times two", data)}
+            {"a": 3.01, "Times two": ("times two", data)}
         )
 
         a = pybamm.Parameter("a")
-        func = pybamm.FunctionParameter("Diffusivity", {"a": a})
+        func = pybamm.FunctionParameter("Times two", {"a": a})
 
         processed_func = parameter_values.process_symbol(func)
         self.assertIsInstance(processed_func, pybamm.Interpolant)
@@ -346,6 +346,16 @@ def test_process_interpolant(self):
         processed_diff_func = parameter_values.process_symbol(diff_func)
         self.assertEqual(processed_diff_func.evaluate(), 2)
 
+        # interpolant defined up front
+        interp2 = pybamm.Interpolant(data, a)
+        processed_interp2 = parameter_values.process_symbol(interp2)
+        self.assertEqual(processed_interp2.evaluate(), 6.02)
+
+        data3 = np.hstack([x, 3 * x])
+        interp3 = pybamm.Interpolant(data3, a)
+        processed_interp3 = parameter_values.process_symbol(interp3)
+        self.assertEqual(processed_interp3.evaluate(), 9.03)
+
     def test_interpolant_against_function(self):
         parameter_values = pybamm.ParameterValues({})
         parameter_values.update(