Originally Posted by

**badgerigar** I'm just doing some practice exam questions and the question asks me to solve

$\displaystyle

\frac{\partial u}{\partial t}+u^2\frac{\partial u}{\partial x} = 0$

with

$\displaystyle u(x,0) = \left\{ \begin{array}{cc} 1, &x<0\\0, &x \geq 0 \end{array} \right.$

I am expected to use the method of characteristics. The calculation was very straightforward and I ended up with

$\displaystyle

u(x,t) = \left\{ \begin{array}{ll} 1,&x<\frac13 t\\0,&x>\frac13 t \end{array} \right.$

What I'm not sure about is the value of $\displaystyle u$ on the shock: does the fact that the initial conditions used $\displaystyle \geq$ instead of > mean that $\displaystyle u=0$ on the shock? or do I need to add to my answer that $\displaystyle u(0,0)=0$