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  2. Dirac delta function - Wikipedia

    en.wikipedia.org/wiki/Dirac_delta_function

    As another example, consider a distribution in which 6/10 of the time returns a standard normal distribution, and 4/10 of the time returns exactly the value 3.5 (i.e. a partly continuous, partly discrete mixture distribution). The density function of this distribution can be written as

  3. Sellmeier equation - Wikipedia

    en.wikipedia.org/wiki/Sellmeier_equation

    For common optical glasses, the refractive index calculated with the three-term Sellmeier equation deviates from the actual refractive index by less than 5×10 −6 over the wavelengths' range [5] of 365 nm to 2.3 μm, which is of the order of the homogeneity of a glass sample. [6]

  4. Group-velocity dispersion - Wikipedia

    en.wikipedia.org/wiki/Group-velocity_dispersion

    A closely related yet independent quantity is the group-delay dispersion (GDD), defined such that group-velocity dispersion is the group-delay dispersion per unit length. GDD is commonly used as a parameter in characterizing layered mirrors, where the group-velocity dispersion is not particularly well-defined, yet the chirp induced after ...

  5. Time derivative - Wikipedia

    en.wikipedia.org/wiki/Time_derivative

    A time derivative is a derivative of a function with respect to time, usually interpreted as the rate of change of the value of the function. [1] The variable denoting time is usually written as t {\displaystyle t} .

  6. Delay differential equation - Wikipedia

    en.wikipedia.org/wiki/Delay_differential_equation

    DDEs are also called time-delay systems, systems with aftereffect or dead-time, hereditary systems, equations with deviating argument, or differential-difference equations. They belong to the class of systems with the functional state , i.e. partial differential equations (PDEs) which are infinite dimensional, as opposed to ordinary ...

  7. Dispersion relation - Wikipedia

    en.wikipedia.org/wiki/Dispersion_relation

    Given the dispersion relation, one can calculate the frequency-dependent phase velocity and group velocity of each sinusoidal component of a wave in the medium, as a function of frequency. In addition to the geometry-dependent and material-dependent dispersion relations, the overarching Kramers–Kronig relations describe the frequency ...

  8. Dirac comb - Wikipedia

    en.wikipedia.org/wiki/Dirac_comb

    The graph of the Dirac comb function is an infinite series of Dirac delta functions spaced at intervals of T. In mathematics, a Dirac comb (also known as sha function, impulse train or sampling function) is a periodic function with the formula ⁡ := = for some given period . [1]

  9. Five-point stencil - Wikipedia

    en.wikipedia.org/wiki/Five-point_stencil

    The first derivative of a function f of a real variable at a point x can be approximated using a five-point stencil as: [1] ′ (+) + (+) + The center point f(x) itself is not involved, only the four neighboring points.