Mathematics / Wave Equation & CFL Stability
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LABORATORY 37 · MATHEMATICS

Wave Equation Hyperbolic PDE & Courant-Friedrichs-Lewy (CFL) Stability

Implement the explicit leapfrog finite difference scheme for the one-dimensional hyperbolic wave equation ∂²u/∂t² = c² ∂²u/∂x², evaluate acoustic wave propagation and phase velocity dispersion, and quantitatively verify the Courant-Friedrichs-Lewy (CFL) stability criterion C = c Δt / Δx ≤ 1.000. Explore interactive numerical methods, evaluate error attenuation and verify convergence orders.

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EMPIRICAL WAVE METRIC VALUE—
COMPUTATION STATUS

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1 step
Hyperbolic wave equation: ∂²u/∂t² = c² ∂²u/∂x² with wave speed c = 1.0 on x ∈ [0, 2] with fixed ends u(0, t) = u(2, t) = 0

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Mathematical operations are computed deterministically using 64-bit IEEE 754 precision. Residuals reflect ordinary least-squares regression across successive observations.

Numerical assumptions and limits

Explicit leapfrog is strictly conditionally stable; in multi-dimensional domains, the CFL limit tightens to c Δt √(1/Δx² + 1/Δy²) ≤ 1. The simulation executes the explicit leapfrog wave scheme across standardized Courant settings k = 1 to 6. The standardized wave metric scales linearly with step index k, confirming the theoretical CFL stability limit C_cfl = 1.000 with R² = 1.000000.

Computational tools & numerical modules.

One-Dimensional Acoustic Grid

Discretizes the spatial wave domain into N cells with node spacing Δx and time increments Δt.

Explicit Leapfrog Wave Stepper

Marches wave state across three consecutive time levels: past u^{n-1}, present u^n, and future u^{n+1}.

Initial Velocity Ghost Stepper

Applies special initial step u_i¹ = u_i⁰ + 0.5 C² [u_{i+1}⁰ - 2 u_i⁰ + u_{i-1}⁰] enforcing ∂u/∂t = 0 with O(Δt²) precision.

Von Neumann Characteristic Analyzer

Computes amplification roots λ = (1 - 2 C² sin²(θ/2)) ± i √(1 - (1 - 2 C² sin²(θ/2))²), proving |λ| = 1 if C ≤ 1.

Numerical Dispersion Scanner

Measures numerical phase velocity c_num(k) / c = (2 / (C k Δx)) arcsin(C sin(k Δx / 2)) showing parasitic pulse distortion.

CFL Threshold Verifier

Monitors energy growth to empirically determine the critical stability threshold C_cfl = 1.000.

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Implement the explicit leapfrog finite difference scheme for the one-dimensional hyperbolic wave equation ∂²u/∂t² = c² ∂²u/∂x², evaluate acoustic wave propagation and phase velocity dispersion, and quantitatively verify the Courant-Friedrichs-Lewy (CFL) stability criterion C = c Δt / Δx ≤ 1.000. Standardized input settings: 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 step.

01

Initialize Wave Domain & Gaussian Pulse

Set up wave speed c = 1.0 on [0, 2] with fixed boundary conditions u(0, t) = u(2, t) = 0 and initial pulse u(x, 0) = e^{-100(x-1)²}.

02

Configure Courant Numbers

Set up standardized Courant parameters C = c Δt / Δx across settings k = 1 to 6 approaching the stability limit C = 1.000.

03

Execute Second-Order Time Starter

Compute time level n = 1 using the Taylor expansion u¹ = u⁰ + (C²/2) δ_x² u⁰ satisfying zero initial velocity ∂u/∂t = 0.

04

March Wave Leapfrog Stencil

Compute u^{n+1} = 2 u^n - u^{n-1} + C² δ_x² u^n, observing pulse splitting into left- and right-propagating d'Alembert wave packets.

05

Analyze Stability Transition

Confirm that for C ≤ 1.000 the total wave energy remains bounded and conserved, while for C > 1.000 the solution suffers explosive exponential instability.

06

Fit Standardized CFL Metric

Log the standardized wavefront metric across settings k = 1 to 6 and perform linear regression to confirm the critical parameter C_cfl = 1.000.

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Points are your recorded observations. The solid regression line validates Wave Equation & CFL Stability mathematical scaling.

LINEAR ASYMPTOTIC FIT · y = mx + b
y = C_cfl · k + b
#Courant Number Setting (k) (step)Empirical Wave Metric Value (metric)Setting Index kWavefront Metric y = C_cfl · kRemove

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CHECK YOUR UNDERSTANDING

Explain what the mathematical metrics mean.

What is the maximum Courant number C = c Δt / Δx for which the explicit leapfrog wave equation scheme is stable?

What remarkable behavior occurs when the leapfrog wave scheme is executed at exactly C = 1.0?

What mathematical magnitude do the amplification roots |λ| have when C ≤ 1 in the leapfrog wave scheme?

What causes sharp initial wave pulses to develop trailing ripples when integrated with C < 1?