Made group action "future concepts"

GTSAM-Concepts.md

@@ -65,32 +65,6 @@ We do *not* at this time support more than one composition operator per type. Al
 
 Also, a type should provide either multiplication or addition operators depending on the flavor of the operation. To distinguish between the two, we will use a tag (see below).
 
-Group Action
-------------
-
-Group actions are concepts in and of themselves that can be concept checked (see below).
-In particular, a group can *act* on another space.
-For example, the [cyclic group of order 6](http://en.wikipedia.org/wiki/Cyclic_group) can rotate 2D vectors around the origin:
-
-    q = R(i)*p
-    where R(i) = R(60)^i, where R(60) rotates by 60 degrees
-    
-Hence, we formalize by the following extension of the concept:
-
-* valid expressions:
-    * `q = traits<T>::Act(g,p)`, for some instance, *p*,  of a space *S*, that can be acted upon by the group element *g* to produce *q* in *S*.
-    * `q = traits<T>::Act(g,p,Hp)`, if the space acted upon is a continuous differentiable manifold. *
-  
-In the latter case, if *S* is an n-dimensional manifold, *Hp* is an output argument that should be 
-filled with the *nxn* Jacobian matrix of the action with respect to a change in *p*. It typically depends
-on the group element *g*, but in most common example will *not* depend on the value of *p*. For example, in 
-the cyclic group example above, we simply have
-
-    Hp = R(i)
-  
-Note there is no derivative of the action with respect to a change in g. That will only be defined
-for Lie groups, which we introduce now.
-
 Lie Group
 ---------
 
@@ -129,22 +103,6 @@ However, the exponential map is unnecessarily expensive for use in optimization.
 
 Most Lie groups we care about are *Matrix groups*, continuous sub-groups of *GL(n)*, the group of *n x n* invertible matrices. In this case, a lot of the derivatives calculations needed can be standardized, and this is done by the `LieGroup` superclass. You only need to provide an `AdjointMap` method.
 
-Lie Group Action
-----------------
-
-When a Lie group acts on a space, we have two derivatives to care about:
-
-  * `gtasm::manifold::traits<T>::act(g,p,Hg,Hp)`, if the space acted upon is a continuous differentiable manifold.
-
-An example is a *similarity transform* in 3D, which can act on 3D space, like
-
-    q = s*R*p + t
-    
-Note that again the derivative in *p*,  *Hp* is simply *s R*, which depends on *g* but not on *p*. 
-The derivative  in *g*,  *Hg*, is in general more complex.
-
-For now, we won't care about Lie groups acting on non-manifolds.
-
 Vector Space
 ------------
 
@@ -198,4 +156,51 @@ Boost provides a nice way to check whether a given type satisfies a concept. For
 
     BOOST_CONCEPT_ASSERT(IsVectorSpace<Point2>)
     
-asserts that Point2 indeed is a model for the VectorSpace concept.
+asserts that Point2 indeed is a model for the VectorSpace concept.
+
+Future Concepts
+===============
+
+
+Group Action
+------------
+
+Group actions are concepts in and of themselves that can be concept checked (see below).
+In particular, a group can *act* on another space.
+For example, the [cyclic group of order 6](http://en.wikipedia.org/wiki/Cyclic_group) can rotate 2D vectors around the origin:
+
+    q = R(i)*p
+    where R(i) = R(60)^i, where R(60) rotates by 60 degrees
+    
+Hence, we formalize by the following extension of the concept:
+
+* valid expressions:
+    * `q = traits<T>::Act(g,p)`, for some instance, *p*,  of a space *S*, that can be acted upon by the group element *g* to produce *q* in *S*.
+    * `q = traits<T>::Act(g,p,Hp)`, if the space acted upon is a continuous differentiable manifold. *
+  
+In the latter case, if *S* is an n-dimensional manifold, *Hp* is an output argument that should be 
+filled with the *nxn* Jacobian matrix of the action with respect to a change in *p*. It typically depends
+on the group element *g*, but in most common example will *not* depend on the value of *p*. For example, in 
+the cyclic group example above, we simply have
+
+    Hp = R(i)
+  
+Note there is no derivative of the action with respect to a change in g. That will only be defined
+for Lie groups, which we introduce now.
+
+
+Lie Group Action
+----------------
+
+When a Lie group acts on a space, we have two derivatives to care about:
+
+  * `gtasm::manifold::traits<T>::act(g,p,Hg,Hp)`, if the space acted upon is a continuous differentiable manifold.
+
+An example is a *similarity transform* in 3D, which can act on 3D space, like
+
+    q = s*R*p + t
+    
+Note that again the derivative in *p*,  *Hp* is simply *s R*, which depends on *g* but not on *p*. 
+The derivative  in *g*,  *Hg*, is in general more complex.
+
+For now, we won't care about Lie groups acting on non-manifolds.