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  2. Square wave - Wikipedia

    en.wikipedia.org/wiki/Square_wave

    The square wave in mathematics has many definitions, which are equivalent except at the discontinuities: It can be defined as simply the sign function of a sinusoid: = ⁡ (⁡) = ⁡ (⁡) = ⁡ (⁡) = ⁡ (⁡), which will be 1 when the sinusoid is positive, −1 when the sinusoid is negative, and 0 at the discontinuities.

  3. List of equations in quantum mechanics - Wikipedia

    en.wikipedia.org/wiki/List_of_equations_in...

    One particle: N particles: One dimension ^ = ^ + = + ^ = = ^ + (,,) = = + (,,) where the position of particle n is x n. = + = = +. (,) = /.There is a further restriction — the solution must not grow at infinity, so that it has either a finite L 2-norm (if it is a bound state) or a slowly diverging norm (if it is part of a continuum): [1] ‖ ‖ = | |.

  4. Wave equation - Wikipedia

    en.wikipedia.org/wiki/Wave_equation

    The wave equation is a second-order linear partial differential equation for the description of waves or standing wave fields such as mechanical waves (e.g. water waves, sound waves and seismic waves) or electromagnetic waves (including light waves). It arises in fields like acoustics, electromagnetism, and fluid dynamics.

  5. List of equations in wave theory - Wikipedia

    en.wikipedia.org/wiki/List_of_equations_in_wave...

    The phase velocity is the rate at which the phase of the wave propagates in space. The group velocity is the rate at which the wave envelope, i.e. the changes in amplitude, propagates. The wave envelope is the profile of the wave amplitudes; all transverse displacements are bound by the envelope profile.

  6. d'Alembert's formula - Wikipedia

    en.wikipedia.org/wiki/D'Alembert's_formula

    The characteristics of the PDE are = (where sign states the two solutions to quadratic equation), so we can use the change of variables = + (for the positive solution) and = (for the negative solution) to transform the PDE to =.

  7. Kirchhoff's diffraction formula - Wikipedia

    en.wikipedia.org/wiki/Kirchhoff's_diffraction...

    A geometrical arrangement used in deriving the Kirchhoff's diffraction formula. The area designated by A 1 is the aperture (opening), the areas marked by A 2 are opaque areas, and A 3 is the hemisphere as a part of the closed integral surface (consisted of the areas A 1, A 2, and A 3) for the Kirchhoff's integral theorem.

  8. Bethe ansatz - Wikipedia

    en.wikipedia.org/wiki/Bethe_ansatz

    The square of the norm of Bethe wave function is equal to the determinant of the Hessian of the Yang action. [3] A substantial generalization is the quantum inverse scattering method, or algebraic Bethe ansatz, which gives an ansatz for the underlying operator algebra that "has allowed a wide class of nonlinear evolution equations to be solved ...

  9. Dirichlet problem - Wikipedia

    en.wikipedia.org/wiki/Dirichlet_problem

    Consider the Dirichlet problem for the wave equation describing a string attached between walls with one end attached permanently and the other moving with the constant velocity i.e. the d'Alembert equation on the triangular region of the Cartesian product of the space and the time: