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Theta functions ${\displaystyle \vartheta (z;\tau )}$ are special functions of several complex variables. Theta function may also refer to:

Jacobi-related functions

• q-theta function, ${\displaystyle \theta (z;q)}$, a type of q-series
• Theta function of a lattice, ${\displaystyle \Theta _{\Lambda }(\tau )}$, a holomorphic function on the upper half-plane
• Mock theta functions, ${\displaystyle \mu (q),f(q),\phi (q),\psi (q),\chi (q)}$, etc., a mock modular form of weight 1/2
• Ramanujan theta function, ${\displaystyle f(a,b)}$
• Neville theta functions

Other functions

• Riemann–Siegel theta function, ${\displaystyle \theta (t)}$
• The first Chebyshev function ${\displaystyle \vartheta (x)}$, the sum of the logarithm of all primes ${\displaystyle \leq x}$
• Feferman's function, ${\displaystyle \theta _{\alpha }(\beta )}$
• Heaviside step function, sometimes denoted ${\displaystyle \theta (x)}$
• Lovász theta function, an upper bound on the Shannon capacity of a graph

See also

• Jacobi theta functions (notational variations), ${\displaystyle \vartheta _{ij}(z;\tau ),\vartheta _{j}(z),\theta _{i}(z;q)}$

• Mathematics disambiguation pages