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  2. Theta function - Wikipedia

    en.wikipedia.org/wiki/Theta_function

    There are several closely related functions called Jacobi theta functions, and many different and incompatible systems of notation for them. One Jacobi theta function (named after Carl Gustav Jacob Jacobi) is a function defined for two complex variables z and τ, where z can be any complex number and τ is the half-period ratio, confined to the upper half-plane, which means it has a positive ...

  3. List of trigonometric identities - Wikipedia

    en.wikipedia.org/wiki/List_of_trigonometric...

    A formula for computing the trigonometric identities for the one-third angle exists, but it requires finding the zeroes of the cubic equation 4x 3 − 3x + d = 0, where is the value of the cosine function at the one-third angle and d is the known value of the cosine function at the full angle.

  4. Trigonometric functions - Wikipedia

    en.wikipedia.org/wiki/Trigonometric_functions

    All of the trigonometric functions of the angle θ (theta) can be constructed geometrically in terms of a unit circle centered at O. Sine function on unit circle (top) and its graph (bottom) In this illustration, the six trigonometric functions of an arbitrary angle θ are represented as Cartesian coordinates of points related to the unit circle.

  5. Ramanujan theta function - Wikipedia

    en.wikipedia.org/wiki/Ramanujan_theta_function

    In mathematics, particularly q-analog theory, the Ramanujan theta function generalizes the form of the Jacobi theta functions, while capturing their general properties. In particular, the Jacobi triple product takes on a particularly elegant form when written in terms of the Ramanujan theta.

  6. Riemann–Siegel theta function - Wikipedia

    en.wikipedia.org/wiki/Riemann–Siegel_theta...

    In mathematics, the Riemann–Siegel theta function is defined in terms of the gamma function as = ⁡ ((+)) ⁡for real values of t.Here the argument is chosen in such a way that a continuous function is obtained and () = holds, i.e., in the same way that the principal branch of the log-gamma function is defined.

  7. Sinc function - Wikipedia

    en.wikipedia.org/wiki/Sinc_function

    The sinc function for a non-Cartesian lattice (e.g., hexagonal lattice) is a function whose Fourier transform is the indicator function of the Brillouin zone of that lattice. For example, the sinc function for the hexagonal lattice is a function whose Fourier transform is the indicator function of the unit hexagon in the frequency space. For a ...

  8. Poisson summation formula - Wikipedia

    en.wikipedia.org/wiki/Poisson_summation_formula

    It can be used to prove the functional equation for the theta function. Poisson's summation formula appears in Ramanujan's notebooks and can be used to prove some of his formulas, in particular it can be used to prove one of the formulas in Ramanujan's first letter to Hardy. [clarification needed] It can be used to calculate the quadratic Gauss ...

  9. Pythagorean trigonometric identity - Wikipedia

    en.wikipedia.org/wiki/Pythagorean_trigonometric...

    By the periodicity identities we can say if the formula is true for −π < θ ≤ π then it is true for all real θ. Next we prove the identity in the range ⁠ π / 2 ⁠ < θ ≤ π. To do this we let t = θ − ⁠ π / 2 ⁠, t will now be in the range 0 < t ≤ π/2. We can then make use of squared versions of some basic shift identities ...