In q-analog theory, the Jackson integral or q-integral is a series in the theory of special functions that expresses the operation inverse to q-differentiation.
The Jackson integral was introduced by Frank Hilton Jackson. For methods of numerical evaluation, see and .
Definition Let f(x) be a function of a real variable x. For a a real variable, the Jackson integral of f is defined by the following series expansion:
Consistent with this is the definition for
More generally, if g(x) is another function and Dqg denotes its q-derivative, we can formally write
or
giving a q-analogue of the Riemann–Stieltjes integral.
Jackson integral as q-antiderivative Just as the ordinary antiderivative of a continuous function can be represented by its Riemann integral, it is possible to show that the Jackson integral gives a unique q-antiderivative within a certain class of functions (see ). Theorem Suppose that If is bounded on the interval for some then the Jackson integral converges to a function on which is a q-antiderivative of Moreover, is continuous at with and is a unique antiderivative of in this class of functions.Kac-Cheung, Theorem 19.1.
Notes
References Victor Kac, Pokman Cheung, Quantum Calculus, Universitext, Springer-Verlag, 2002. Jackson F H (1904), "A generalization of the functions Γ(n) and xn", Proc. R. Soc. 74 64–72. Jackson F H (1910), "On q-definite integrals", Q. J. Pure Appl. Math. 41 193–203.