Synopsis
		sfheatimplitest > out.rsf nt= dt= nx= dx=

\partial(u)/\partial(t)=a^2\partial^2(u)/\partial(x^2), 00,
u(0,t)=u(l,t)=0, t>0,
u(x,0)=f(x), 0<=x<=l.

Parameters
		float dt= temporal sampling   float dx= spatial sampling   int nt= number of temporal points   int nx= number of spatial points