add exponential method for real tangent vectors

[[Imported from SVN: r8115]]

dune/gfe/rotation.hh

@@ -267,6 +267,20 @@ public:
         
         // The actual exponential map
         return exp(p, vMatrix);
+    }
+     /** \brief The exponential map from a given point $p \in SO(3)$.
+     
+        \param v A tangent vector.
+     */
+    static Rotation<3,T> exp(const Rotation<3,T>& p, const TangentVector& v) {
+        
+        // embedded tangent vector
+        Dune::FieldMatrix<T,3,4> basis = p.orthonormalFrame();
+        Quaternion<T> embeddedTangent;
+        basis.mtv(v, embeddedTangent);
+        
+        return exp(p,embeddedTangent);
+
     }
        
     /** \brief Compute tangent vector from given basepoint and skew symmetric matrix. */