heat2.jl

using DiffEqOperators, DifferentialEquations, Plots

# # Heat Equation
# This example demonstrates how to combine `OrdinaryDiffEq` with `DiffEqOperators` to solve a time-dependent PDE.
# We consider the heat equation on the unit interval, with Dirichlet boundary conditions:
# ∂ₜu = Δu
# u(x=0,t)  = a
# u(x=1,t)  = b
# u(x, t=0) = u₀(x)
#
# For `a = b = 0` and `u₀(x) = sin(2πx)` a solution is given by:
u_analytic(x, t) = sin(2*π*x) * exp(-t*(2*π)^2)

nknots = 100
h = 1.0/(nknots+1)
knots = range(h, step=h, length=nknots)
ord_deriv = 2
ord_approx = 2

const Δ = CenteredDifference(ord_deriv, ord_approx, h, nknots)
const bc = Dirichlet0BC(Float64)

t0 = 0.0
t1 = 0.03
u0 = u_analytic.(knots, t0)

step(u,p,t) = Δ*bc*u
prob = ODEProblem(step, u0, (t0, t1))
alg = KenCarp4()
sol = solve(prob, alg)

plot(knots,sol(0.0),label="0.0") 
plot!(knots,sol(0.1))
plot!(knots,sol(0.2))
plot!(knots,sol(0.3))