Fix rotateby documentation (#2903)

* Fixes #2901
* Changes made in this Pull Request:
    - Added call to rotateby (instead of rotate)
    - Removed () from atom group

package/MDAnalysis/transformations/rotate.py

@@ -43,35 +43,39 @@
 
 def rotateby(angle, direction, point=None, ag=None, weights=None, wrap=False):
     '''
-    Rotates the trajectory by a given angle on a given axis. The axis is defined by 
+    Rotates the trajectory by a given angle on a given axis. The axis is defined by
     the user, combining the direction vector and a point. This point can be the center
-    of geometry or the center of mass of a user defined AtomGroup, or an array defining 
+    of geometry or the center of mass of a user defined AtomGroup, or an array defining
     custom coordinates.
-    
+
     Examples
     --------
-    
-    e.g. rotate the coordinates by 90 degrees on a axis formed by the [0,0,1] vector and 
+
+    e.g. rotate the coordinates by 90 degrees on a axis formed by the [0,0,1] vector and
     the center of geometry of a given AtomGroup:
-    
+
     .. code-block:: python
-    
+
+        from MDAnalysis import transformations
+
         ts = u.trajectory.ts
         angle = 90
-        ag = u.atoms()
+        ag = u.atoms
         d = [0,0,1]
-        rotated = MDAnalysis.transformations.rotate(angle, direction=d, ag=ag)(ts)
-    
+        rotated = transformations.rotate.rotateby(angle, direction=d, ag=ag)(ts)
+
     e.g. rotate the coordinates by a custom axis:
-    
+
     .. code-block:: python
 
+        from MDAnalysis import transformations
+
         ts = u.trajectory.ts
         angle = 90
         p = [1,2,3]
         d = [0,0,1]
-        rotated = MDAnalysis.transformations.rotate(angle, direction=d, point=point)(ts) 
-    
+        rotated = transformations.rotate.rotateby(angle, direction=d, point=p)(ts)
+
     Parameters
     ----------
     angle: float
@@ -100,7 +104,7 @@ def rotateby(angle, direction, point=None, ag=None, weights=None, wrap=False):
     Returns
     -------
     MDAnalysis.coordinates.base.Timestep
-    
+
     Warning
     -------
     Wrapping/unwrapping the trajectory or performing PBC corrections may not be possible 
@@ -138,7 +142,7 @@ def rotateby(angle, direction, point=None, ag=None, weights=None, wrap=False):
         center_method = partial(atoms.center, weights, pbc=wrap)
     else:
         raise ValueError('A point or an AtomGroup must be specified')
-    
+
     def wrapped(ts):
         if point is None:
             position = center_method()
@@ -149,8 +153,8 @@ def wrapped(ts):
         translation = matrix[:3, 3]
         ts.positions= np.dot(ts.positions, rotation)
         ts.positions += translation
-        
+
         return ts
-    
+
     return wrapped
-    
+