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  2. Dirac delta function - Wikipedia

    en.wikipedia.org/wiki/Dirac_delta_function

    In mathematical analysis, the Dirac delta function (or δ distribution), also known as the unit impulse, [1] is a generalized function on the real numbers, whose value is zero everywhere except at zero, and whose integral over the entire real line is equal to one.

  3. Duhamel's integral - Wikipedia

    en.wikipedia.org/wiki/Duhamel's_integral

    If a system initially rests at its equilibrium position, from where it is acted upon by a unit-impulse at the instance t=0, i.e., p(t) in the equation above is a Dirac delta function δ(t), () = | = =, then by solving the differential equation one can get a fundamental solution (known as a unit-impulse response function)

  4. Heaviside step function - Wikipedia

    en.wikipedia.org/wiki/Heaviside_step_function

    Hence the Heaviside function can be considered to be the integral of the Dirac delta function. This is sometimes written as H ( x ) := ∫ − ∞ x δ ( s ) d s {\displaystyle H(x):=\int _{-\infty }^{x}\delta (s)\,ds} although this expansion may not hold (or even make sense) for x = 0 , depending on which formalism one uses to give meaning to ...

  5. Unit doublet - Wikipedia

    en.wikipedia.org/wiki/Unit_doublet

    Approximation of a unit doublet with two rectangles of width k as k goes to zero. In mathematics, the unit doublet is the derivative of the Dirac delta function.It can be used to differentiate signals in electrical engineering: [1] If u 1 is the unit doublet, then

  6. Common integrals in quantum field theory - Wikipedia

    en.wikipedia.org/wiki/Common_integrals_in...

    The Dirac delta distribution in spacetime can be written as a Fourier transform [1]: ... The two-dimensional integral over a magnetic wave function is [6]: ...

  7. Feynman parametrization - Wikipedia

    en.wikipedia.org/wiki/Feynman_parametrization

    If A(p) and B(p) are linear functions of p, then the last integral can be evaluated using substitution. More generally, using the Dirac delta function δ {\displaystyle \delta } : [ 2 ]

  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. Green's function - Wikipedia

    en.wikipedia.org/wiki/Green's_function

    Then the integral (′) (′) ′ reduces to simply φ(x) due to the defining property of the Dirac delta function and we have = (, ′) (′) ′ + [(′) ′ (, ′) (, ′) ′ (′)] ^ ′. This form expresses the well-known property of harmonic functions , that if the value or normal derivative is known on a bounding surface, then the ...