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User:Harry Princeton/Chain Integrals and Higher-Order Integrals

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This is my work on Chain Integration and Integration by Parts (higher-order integrals). Also included is a differential analysis on cycloids.

Chain Integration Formula and Examples

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See Fresnel integral.

We could approximate the tangent and secant integrals

and

by using the Cauchy Principal Value and integration by parts:

and

with the square Chain Integration formula where .

In fact, integrals through CPV are defined when subtracting balanced pole functions - pure powers of - from original poles, results in functions with remaining possible singularities of size with strict).

Notice that both and have simple nonzero isolated poles, limiting to scalar multiples of . Then and with .

Therefore, is bounded for and ; as we have the related bounded integral and we can do scalar multiple comparisons. So by CPV, the above integrals are defined except at isolated poles. Graphs of these integrals for are found below:

Graphs of and
Integral of Tan x^2 Integral of Sec x^2
[0,15] × [-5, 5] [0,15] × [-5, 5]

Finally, we have, approximately:

compared to for both and .

Modulated Integrals

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We could also approximate the cotangent and cosecant integrals

and

by using an integration by parts, but need to isolate a pole of order 2 at for each function. We do so by subtracting from each function to yield bounded functions at (in fact, with for both functions!), applying the same treatment as previously (it works similarly at all other poles), and then adding the antiderivative of back.

Since both integrals have right limit as approaches , we instead add constants so that critical points/inflection points of the cotangent/cosecant integrals, respectively, approach as (canonicalization). We thus have:

With graphs seen below:

Graphs of and
Integral of Cot x^2 Integral of csc x^2
[0,15] × [-5, 5] [0,15] × [-5, 5]

Higher Order (Stacked) Integrals

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A general formula for the second-order real integral (second antiderivative) is

A general formula for the third-order real integral (third antiderivative) is

A general formula for the th-order real integral (th antiderivative) is

So to compute higher-order integrals, no other nonelementary integrals need to be considered except for those possibly equal to for (Riemann-integrable functions). To compute from another bound , it is sufficient for integrals only of the form to be considered.

Example

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Below, the first five antiderivatives of are computed and graphed, using this method. Since is undefined at (in fact, is an essential singularity, and every antiderivative diverges as ), we start at instead (a critical minimum point for , so most suitable):

Note that the general chain integral formula cannot be used since (1) is not strictly monotone, (2) no balanced essential singularity can be isolated from , not even , and (3) even the balanced essential singularity is not elementary-integrable.

Graphs of Five Antiderivatives of
Square Window Vertical Rectangular Window
[-9,9] × [-3.478, 10.432] [-3.3,3.3] × [-50, 50]

Cycloid

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The work-energy formula is intrinsic to any twice continuously differentiable increasing function:

This is by Chain Rule, since for any twice continuously differentiable increasing function .

Using the work-energy formula

with , initial position , and initial velocity ; we have

by the Fundamental Theorem of Calculus I. So in fact the cycloid is the solution to Newton's Gravitational Law (where time is measured in ) if a particle is bounded in a heavy point object's gravitational field (negative net energy), with zero angular momentum; if we set , , to obtain .

Other zero-angular-momentum solutions for identical mass include for zero net energy, and for positive net energy. For the first case, indeed

by the Power Rule, where the additional constant of is specific to the cycloid only (which is the total energy); and for the second case, indeed

by the parametric derivative, and the additional constant of is specific to this second path only (which is the total energy).