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Change of variable in an improper integral
Statement
Let and be intervals, possibly open at finite or infinite singular ends, and let be a monotone differentiable surjection. Assume is locally Riemann integrable and the proper change-of-variable hypotheses hold on every compact truncation. If is locally Riemann integrable on , then converge simultaneously and, when convergent, are equal. At several singular ends this assertion is applied separately to the corresponding ends; orientation is retained for decreasing parametrizations.
Facts & Assumptions
Given: The intervals, monotone surjection , and locally integrable in the statement.
The proper change-of-variable theorem gives equality on corresponding compact truncations (Monotone change of variable for Riemann-integrable functions).
Monotonicity and surjectivity send truncations tending to an endpoint of to truncations tending to the corresponding endpoint of .
Improper convergence at one end is the existence of a finite limit of the corresponding compact-truncation values (Improper integrals over unbounded intervals, Improper integrals at a finite singular endpoint).
Mixed improper integrals require separate convergence at every singular end (Improper integrals with several singular ends).
Proof
On each compact source truncation , [L1] gives [L1] with the endpoint order adjusted when decreases.
By [L2], the two sides form the same family of values as the corresponding truncation approaches a singular end. Since they are equal term by term by step 1.1, the epsilon condition in [L3] holds for one family exactly when it holds for the other, with the same limit.
For multiple ends, apply step 2.1 separately at each matched end and add only after all pieces converge, as [L4] requires. The oriented convention supplies the sign for a decreasing parametrization.
Depends on
- Monotone change of variable for Riemann-integrable functions
- Improper integrals over unbounded intervals
- Improper integrals at a finite singular endpoint
- Improper integrals with several singular ends
- Nondecreasing, increasing (strictly increasing), nonincreasing, decreasing, monotone and strictly monotone real functions on a subset of $\mathbb{R}$, with the dictionary to monotone sequences
- The derivative $f'(c) = \lim_{x \to c} \frac{f(x) - f(c)}{x - c}$ of $f : A \to \mathbb{R}$ at a point $c \in A$ that is a limit point of $A$, and differentiability on a set
- The integral with oriented limits: $\int_a^a f := 0$ and $\int_b^a f := -\int_a^b f$
Used by
- The closed form for the volume of the unit n-ball Corollary
- Γ(1/2)=√π from the Gaussian integral Corollary
- Differentiation under an improper integral can fail without uniform domination Counterexample
- Iid strong law fails at infinite absolute mean Counterexample
- The complementarity product needs extra regularity Counterexample
- The critical Riesz potential can diverge and be essentially unbounded Counterexample
- A Caputo startup singularity and a graded-grid calculation Example
- An exact Gaussian Laplace integral on the noncompact line Example
- The positive-type Gaussian on the real line and its cyclic model Example
- The scaled Gaussian integral and its parameter derivative Example
- The substitution x=1/t exchanges the two rational p-tests Example
- Vanishing viscosity selects the Hopf--Lax solution for bounded data Example
- A deterministic-prefix envelope sum for the sharper UCB count bound Lemma
- A normal variable has finite fourth moment Lemma
- A one-coordinate projection risk bound Lemma
- Cartesian Gaussian moments and exponent-parameter derivatives Lemma
- Gaussian integral for a positive-definite quadratic form Lemma
- Holomorphic Morse normalization and Gaussian contour Lemma
- Integral of the fractional power kernel Lemma
- Integral representations and a range bound for integer Bessel functions Lemma
- Moment recurrence for the scaled complementary error function Lemma
- Parallel Gaussian information density obeys a finite-variance law of large numbers Lemma
- Semigroup law for fractional integrals Lemma
- Signed finite remainder for the erfcx asymptotic expansion Lemma
- Standard-normal CDF, tail, and quantile identities for power calculations Lemma
- The Hilbert transform is the tempered convolution with pv(1/(pi x)) and has signum Fourier multiplier Lemma
- The improper integral of e^-x² over ℝ is finite and positive Lemma
- The sine integral under Countable Choice: uniform bounds and the value pi/2 Lemma
- The standard normal CDF has unique symmetric quantiles Lemma
- Weierstrass log-Gamma series converges to a Gamma branch Lemma
- Weighted monomial integrals and monomial norms for the disc, ball and polydisc Lemma
- Symmetry and the trigonometric form of the real Beta integral Proposition
- Boys integral, power series, recurrence, and incomplete-gamma representation Theorem
- Hermite recurrence formulas for Gaussian nuclear-attraction and two-electron Coulomb integrals Theorem
- Khintchine's inequality for finite Rademacher sums Theorem
- Positive Coulomb bilinear form, Cauchy–Schwarz, and screening bound Theorem
- The real Gamma function is smooth and its derivatives are logarithmic moments Theorem
Dependency tree · two levels
32 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- William F. Trench, Introduction to Real Analysis, Theorem 3.4.13 (standard reference, not scraped)