例 X-x Sx≤x+x2 x1+x2 00(x 2 v(x)=0 lo 2 u(x, t) x<x, or,x>x2 p(x) x 2 u(x, t=L(x+at)+o(x-at )1例              + − − +   − − = 1 2 2 1 2 2 1 1 0 1 2 1 2 1 1 0 0 , , 2 2 , 2 2 , ( ) x x or x x x x x x x x x x u x x x x x x x x u  x  (x) = 0 (x) x 1 x 2 x 2 1 2 x + x 0 u x u0 ( ) 2 1  x x u(x,t) 1 x 2 x x [ ( ) ( )] 2 1 u(x,t) =  x + at + x − at