Eikonal equation

The Eikonal equation is a fundamental equation in the field of geometric optics and wave propagation. It is typically expressed in the form: \[ |\nabla u(x)| = n(x) \] where \( u(x) \) is the wavefront (or phase) function, \( \nabla u \) denotes the gradient of this function, and \( n(x) \) represents the refractive index at point \( x \) in space.