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In mathematical analysis, an improper integral is an extension of the notion of a definite integral to cases that violate the usual assumptions for that kind of integral. [1] In the context of Riemann integrals (or, equivalently, Darboux integrals ), this typically involves unboundedness, either of the set over which the integral is taken or of ...
In mathematics, the Cauchy principal value, named after Augustin-Louis Cauchy, is a method for assigning values to certain improper integrals which would otherwise be undefined. In this method, a singularity on an integral interval is avoided by limiting the integral interval to the non singular domain.
In mathematics, the comparison test, sometimes called the direct comparison test to distinguish it from similar related tests (especially the limit comparison test), provides a way of deducing whether an infinite series or an improper integral converges or diverges by comparing the series or integral to one whose convergence properties are known.
The fundamental theorem of calculus establishes the relationship between indefinite and definite integrals and introduces a technique for evaluating definite integrals. If the interval is infinite the definite integral is called an improper integral and defined by using appropriate limiting procedures. for example:
Limits of integration can also be defined for improper integrals, with the limits of integration of both + and again being a and b. For an improper integral ∫ a ∞ f ( x ) d x {\displaystyle \int _{a}^{\infty }f(x)\,dx} or ∫ − ∞ b f ( x ) d x {\displaystyle \int _{-\infty }^{b}f(x)\,dx} the limits of integration are a and ∞, or − ...
where the integral on the right is an ordinary improper Riemann integral (f ∗ is a strictly decreasing positive function, and therefore has a well-defined improper Riemann integral). [27] For a suitable class of functions (the measurable functions) this defines the Lebesgue integral.
The improper integral of the Complete Elliptic Integral of first kind K takes the value of twice the Catalan constant accurately. The antiderivative of that K-integral belongs to the so-called Elliptic Polylogarithms. The Catalan constant can only be obtained via the Arctangent Integral, which results from the application of Fubini's theorem:
In this case, the improper definite integral can be determined in several ways: the Laplace transform, double integration, differentiating under the integral sign, contour integration, and the Dirichlet kernel. But since the integrand is an even function, the domain of integration can be extended to the negative real number line as well.