added .sum and .vdot method to operator and used them in energy_operators.py

nifty6/operators/energy_operators.py

@@ -134,10 +134,8 @@ class VariableCovarianceGaussianEnergy(EnergyOperator):
         lin = isinstance(x, Linearization)
         r = FieldAdapter(self._domain[self._r], self._r)
         icov = FieldAdapter(self._domain[self._icov], self._icov)
-        res0 = r.conjugate()*r*icov
-        sum_it = ContractionOperator(res0.target, None)
-        res0 = sum_it(res0).real
-        res1 = sum_it(icov.log())
+        res0 = r.vdot(r*icov).real
+        res1 = icov.log().sum()
         res = 0.5*(res0-res1)
         res = res(x)
         if not lin:

nifty6/operators/operator.py

@@ -66,6 +66,13 @@ class Operator(metaclass=NiftyMeta):
         from .simple_linear_operators import ConjugationOperator
         return ConjugationOperator(self.target)(self)
 
+    def sum(self, spaces=None):
+        from .contraction_operator import ContractionOperator
+        return ContractionOperator(self.target, spaces)(self)
+
+    def vdot(self, other):
+        return (self.conjugate()*other).sum()
+
     @property
     def real(self):
         from .simple_linear_operators import Realizer