wavelength of the wave, which is reflected by a dispersion relation where is the angular frequency and is the wavevector describing plane wave solutions. For light waves, the dispersion relation is , but in general, the constant speed gets replaced by a variable phase velocity: See also Acoustic attenuation Acoustic wave equation Bateman transform Electromagnetic wave equation Helmholtz equation Inhomogeneous electromagnetic wave equation Laplace operator Mathematics of oscillation Maxwell's equations One-way wave equation Schrödinger equation Standing wave Vibrations of a circular membrane Wheeler–Feynman absorber theory Notes References M. F. Atiyah, R. Bott, L. Garding, "Lacunas for hyperbolic differential operators with constant coefficients I", Acta Math., 124 (1970), 109–189. M.F. Atiyah, R. Bott, and L. Garding, "Lacunas for hyperbolic differential operators with constant coefficients II", Acta Math., 131 (1973), 145–206. R. Courant, D. Hilbert, Methods of Mathematical Physics, vol II. Interscience (Wiley) New York, 1962. L. Evans, "Partial Differential Equations". American Mathematical Society Providence, 1998. "Linear Wave Equations", EqWorld: The World of Mathematical Equations. "Nonlinear Wave Equations", EqWorld: The World of Mathematical Equations. William C. Lane, "MISN-0-201 The Wave Equation and Its Solutions", Project PHYSNET. External links Nonlinear Wave Equations by Stephen Wolfram and Rob Knapp, Nonlinear Wave Equation Explorer by Wolfram Demonstrations Project. Mathematical aspects of wave equations are discussed on the Dispersive PDE Wiki . Graham W Griffiths and William E. Schiesser (2009). Linear and nonlinear waves. Scholarpedia, 4(7):4308. doi:10.4249/scholarpedia.4308 Equations of physics Hyperbolic partial differential equations Wave mechanics