remove unused attribute

nifty/operators/diagonal_operator/diagonal_operator.py

@@ -107,17 +107,6 @@ class DiagonalOperator(EndomorphicOperator):
         """
         return self._diagonal.copy() if copy else self._diagonal
 
-    def inverse_diagonal(self):
-        """ Returns the inverse-diagonal of the operator.
-
-        Returns
-        -------
-        out : Field
-            The inverse of the diagonal of the Operator.
-
-        """
-        return 1./self._diagonal
-
     # ---Mandatory properties and methods---
 
     @property

test/test_operators/test_diagonal_operator.py

@@ -84,10 +84,3 @@ class DiagonalOperator_Tests(unittest.TestCase):
         D = DiagonalOperator(diag, copy=copy)
         diag_op = D.diagonal()
         assert_allclose(diag.val, diag_op.val)
-
-    @expand(product(spaces, [True, False]))
-    def test_inverse(self, space, copy):
-        diag = Field.from_random('normal', domain=space)
-        D = DiagonalOperator(diag, copy=copy)
-        diag_op = D.inverse_diagonal()
-        assert_allclose(1./diag.val, diag_op.val)