Here we de¯ne the orders of accuracy of the schemes. Let u be the solution on ­ = [0; L] £ [0; T ] with some prescribed T > 0, and U (m) (0 · m · M; M¢t = T ) be the corresponding numerical solution obtained by a numerical scheme. Then, the global orders of accuracy of the numerical solution (and accordingly of the scheme) are de¯ned as follows. In the de¯nition, we denote some vector norms as k ¢ k.