param dx=1
f(x)=x*(1-x)*(x-0.1)
V0'=(V1-V0)/(dx*dx)+f(V0)
V[1..39]'=(V[j+1]-2*V[j]+V[j-1])/(dx*dx)+f(V[j])
V40'=(V39-V40)/(dx*dx)+f(V40)
init V[0..30]=0
init V31=0.1
init V[32..40]=0.2