Homework Statement
Suppose that u(x,t) satisfies the heat equation u_{t}=u_{x x} for 0<x<L and t>0 with initial condition u(x,0)=θ(x) and boundary conditions u(0,t)=u(L,t)=0. Suppose that θ(x)>0 for 0<x<L. Explain why u(x,t)>0 for all 0<x<L and t>0
Homework Equations
Strong Maximum principle...