Fix the alias operator constructors on Ga objects

Previously:

* `Ga.pdop` was unusable, since it would call `Pdop.__init__` with a `tuple`, but that function expects a `Symbol` or `Dict`
* `Ga.sdop` was not callable with one argument, since it would pass on an unwanted `None` argument to `pdiffs`

Also groups these functions to be adjacent, for clarity

Author: eric-wieser

galgebra/ga.py

@@ -516,9 +516,6 @@ def mv_x(self):
     def X(self):
         return self.mv(sum([coord*base for (coord, base) in zip(self.coords, self.basis)]))
 
-    def sdop(self, coefs, pdiffs=None):
-        return mv.Sdop(coefs, pdiffs, ga=self)
-
     def mv(self, root=None, *args, **kwargs):
         """
         Instanciate and return a multivector for this, 'self',
@@ -612,13 +609,17 @@ def grads(self):
             raise ValueError("Ga must have been initialized with coords to compute grads")
         return self.grad, self.rgrad
 
+    def pdop(self, *args, **kwargs):
+        """ Shorthand to construct a :class:`~galgebra.mv.Pdop` for this algebra """
+        return mv.Pdop(*args, ga=self, **kwargs)
+
     def dop(self, *args, **kwargs):
-        """
-        Instanciate and return a multivector differential operator for
-        this, 'self', geometric algebra.
-        """
-        kwargs['ga'] = self
-        return mv.Dop(*args, **kwargs)
+        """ Shorthand to construct a :class:`~galgebra.mv.Dop` for this algebra """
+        return mv.Dop(*args, ga=self, **kwargs)
+
+    def sdop(self, *args, **kwargs):
+        """ Shorthand to construct a :class:`~galgebra.mv.Sdop` for this algebra """
+        return mv.Sdop(*args, ga=self, **kwargs)
 
     def lt(self, *args, **kwargs):
         """
@@ -1710,9 +1711,6 @@ def blade_derivation(self, blade, ib):
         self._dbases[key] = db
         return db
 
-    def pdop(self,*args):
-        return mv.Pdop(args,ga=self)
-
     def pDiff(self, A, coord):
         """
         Compute partial derivative of multivector function 'A' with