Fixing SparseGridGPU serialization

src/SparseGridGpu/SparseGridGpu.hpp

@@ -2829,7 +2829,13 @@ public:
 	//Functions to check if the packing object is complex
 	static bool pack()
 	{
-		return false;
+		return true;
+	}
+
+	//Functions to check if the packing object is complex
+	static bool packRequest()
+	{
+		return true;
 	}
 
 	/*! \brief Asking to pack a SparseGrid GPU without GPU context pack the grid on CPU and host memory

src/Vector/map_vector_std.hpp

@@ -1006,6 +1006,18 @@ public:
 		return base_type::get(id);
 	}
 
+	/*! \brief Get an element of the vector
+	 *
+	 * \param id element to get
+	 *
+	 * \return the element reference
+	 *
+	 */
+	inline T & operator[](size_t id)
+	{
+		return base_type::get(id);
+	}
+
 	/*! \brief Get an element of the vector
 	 *
 	 * \param id element to get