Added sanity check for addition operator, to make sure the two spline…

…s added share the same underlying triangle, and the same degree.

SSplines/spline_function.py

@@ -1,16 +1,19 @@
 import numpy as np
 
 from SSplines.constants import UY, UX
-from SSplines.helper_functions import coefficients_linear, coefficients_quadratic, coefficients_quadratic_alternative, coefficients_cubic, \
-    barycentric_coordinates, determine_sub_triangle, evaluate_non_zero_basis_splines, evaluate_non_zero_basis_derivatives, \
+from SSplines.helper_functions import coefficients_linear, coefficients_quadratic, coefficients_quadratic_alternative, \
+    coefficients_cubic, \
+    barycentric_coordinates, determine_sub_triangle, evaluate_non_zero_basis_splines, \
+    evaluate_non_zero_basis_derivatives, \
     directional_coordinates
 
+
 class SplineFunction(object):
     """
     Represents a single callable spline function of degree 0/1/2/3 over the PS12-split of given triangle.
     """
 
-    def __init__(self, triangle, degree, coefficients, alternative_basis = False):
+    def __init__(self, triangle, degree, coefficients, alternative_basis=False):
         self.triangle = np.array(triangle)
         self.degree = int(degree)
         self.coefficients = np.array(coefficients)
@@ -23,18 +26,18 @@ def _non_zero_coefficients(self, k):
         :return : indices
         """
         if self.degree == 0:
-            return np.take(np.append(self.coefficients,0), k)
+            return np.take(np.append(self.coefficients, 0), k)
         elif self.degree == 1:
-            return np.take(np.append(self.coefficients,0), coefficients_linear(k))
+            return np.take(np.append(self.coefficients, 0), coefficients_linear(k))
         elif self.degree == 2:
             if self.alternative_basis:
-                return np.take(np.append(self.coefficients,0), coefficients_quadratic_alternative(k))
+                return np.take(np.append(self.coefficients, 0), coefficients_quadratic_alternative(k))
             else:
-                return np.take(np.append(self.coefficients,0), coefficients_quadratic(k))
+                return np.take(np.append(self.coefficients, 0), coefficients_quadratic(k))
         elif self.degree == 3:
-            return np.take(np.append(self.coefficients,0), coefficients_cubic(k))
+            return np.take(np.append(self.coefficients, 0), coefficients_cubic(k))
 
-    def __call__(self, x, barycentric = False, exact = False):
+    def __call__(self, x, barycentric=False, exact=False):
         """
         Evaluates the spline function at point(s) x.
         :param x: set of points
@@ -43,10 +46,11 @@ def __call__(self, x, barycentric = False, exact = False):
         if barycentric:
             b = x
         else:
-            b = barycentric_coordinates(self.triangle, x, exact = exact)
+            b = barycentric_coordinates(self.triangle, x, exact=exact)
 
         k = determine_sub_triangle(b)
-        z = evaluate_non_zero_basis_splines(b=b, d=self.degree, k=k, exact = exact, alternative_basis = self.alternative_basis)
+        z = evaluate_non_zero_basis_splines(b=b, d=self.degree, k=k, exact=exact,
+                                            alternative_basis=self.alternative_basis)
         c = self._non_zero_coefficients(k)
 
         return np.einsum('...i,...i->...', z, c)  # broadcast the dot product to compute all values at once.
@@ -132,15 +136,16 @@ def lapl(self, x):
         """
         return self.ddx(x) + self.ddy(x)
 
-    # MATHEMATICAL OPERATORS
-    # TODO: Check degree and triangle for each of these operations
-
     def __add__(self, other):
         """
         Addition of two SplineFunctions.
         :param other: Spline Function
         :return: SplineFunction
         """
+
+        if self.degree != other.degree or not np.allclose(self.triangle, other.triangle):
+            raise ValueError('The splines are not compatible, check the degree and the underlying triangle')
+
         return SplineFunction(self.triangle, self.degree, self.coefficients + other.coefficients)
 
     def __mul__(self, scalar):
@@ -149,4 +154,5 @@ def __mul__(self, scalar):
         :param scalar: real number
         :return: SplineFunction
         """
-        return SplineFunction(self.triangle, self.degree, scalar * self.coefficients)
+
+        return SplineFunction(self.triangle, self.degree, scalar * self.coefficients)

tests/test_spline_operators.py

@@ -0,0 +1,39 @@
+import pytest
+import numpy as np
+
+from SSplines import SplineFunction, SplineSpace
+
+
+def test_spline_function_add_validation():
+    t1 = np.array([
+        [0, 0],
+        [1, 0],
+        [0.5, np.sqrt(3) / 2]
+    ])
+    t2 = np.array([
+        [0, 0],
+        [1, 0],
+        [0.6, np.sqrt(3) / 2]
+    ])
+
+    c1 = np.ones(12)
+    c2 = np.ones(12)
+    c3 = np.ones(10)
+    d1 = 2
+    d2 = 2
+    d3 = 1
+
+    s1 = SplineFunction(t1, d1, c1)
+    s2 = SplineFunction(t2, d2, c2)
+    s3 = SplineFunction(t2, d3, c3)
+
+    with pytest.raises(ValueError):
+        s1 + s2
+
+    with pytest.raises(ValueError):
+        s2 + s3
+
+    try:
+        s1 + s1
+    except ValueError:
+        pytest.fail('An error is raised when the splines are compatible.')