New method: iterative system growth

[oameye]

Implement a new method which compute the solution by iteratively increasing the system size, i.e, first solve x1=[u1,v1,0,0,0,0], Then solve x2=[u1,v1,v2,v2,0,0], starting from the solution of x1, then solve x3=[u1,v1,v2,v2,u3,v3], starting from the solution of x2.