Change default reduction in SystemEquation (#317)

* Update system_equation.py
* Update test_systemequation.py

pina/equation/system_equation.py

@@ -7,7 +7,7 @@ from ..utils import check_consistency
 
 class SystemEquation(Equation):
 
-    def __init__(self, list_equation, reduction="mean"):
+    def __init__(self, list_equation, reduction=None):
         """
         System of Equation class for specifing any system
         of equations in PINA.
@@ -19,14 +19,13 @@ class SystemEquation(Equation):
         :param Callable equation: A ``torch`` callable equation to
             evaluate the residual
         :param str reduction: Specifies the reduction to apply to the output:
-            ``none`` | ``mean`` | ``sum``  | ``callable``. ``none``: no reduction
-            will be applied, ``mean``: the sum of the output will be divided
+            None | ``mean`` | ``sum``  | callable. None: no reduction
+            will be applied, ``mean``: the output sum will be divided
             by the number of elements in the output, ``sum``: the output will
-            be summed. ``callable`` a callable function to perform reduction,
-            no checks guaranteed. Default: ``mean``.
+            be summed. *callable* is a callable function to perform reduction,
+            no checks guaranteed. Default: None.
         """
         check_consistency([list_equation], list)
-        check_consistency(reduction, str)
 
         # equations definition
         self.equations = []
@@ -38,7 +37,7 @@ class SystemEquation(Equation):
             self.reduction = torch.mean
         elif reduction == "sum":
             self.reduction = torch.sum
-        elif (reduction == "none") or callable(reduction):
+        elif (reduction == None) or callable(reduction):
             self.reduction = reduction
         else:
             raise NotImplementedError(
@@ -72,7 +71,7 @@ class SystemEquation(Equation):
             ]
         )
 
-        if self.reduction == "none":
+        if self.reduction is None:
             return residual
 
         return self.reduction(residual, dim=-1)

tests/test_equations/test_systemequation.py

@@ -39,7 +39,7 @@ def test_residual():
     u = torch.pow(pts, 2)
     u.labels = ['u1', 'u2']
 
-    eq_1 = SystemEquation([eq1, eq2])
+    eq_1 = SystemEquation([eq1, eq2], reduction='mean')
     res = eq_1.residual(pts, u)
     assert res.shape == torch.Size([10])
 
@@ -47,6 +47,10 @@ def test_residual():
     res = eq_1.residual(pts, u)
     assert res.shape == torch.Size([10])
 
-    eq_1 = SystemEquation([eq1, eq2], reduction='none')
+    eq_1 = SystemEquation([eq1, eq2], reduction=None)
+    res = eq_1.residual(pts, u)
+    assert res.shape == torch.Size([10, 3])
+
+    eq_1 = SystemEquation([eq1, eq2])
     res = eq_1.residual(pts, u)
     assert res.shape == torch.Size([10, 3])