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1989 | Buch

Elliptic Functions and Applications

verfasst von: Derek F. Lawden

Verlag: Springer New York

Buchreihe : Applied Mathematical Sciences

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Über dieses Buch

The subject matter of this book formed the substance of a mathematical se am which was worked by many of the great mathematicians of the last century. The mining metaphor is here very appropriate, for the analytical tools perfected by Cauchy permitted the mathematical argument to penetra te to unprecedented depths over a restricted region of its domain and enabled mathematicians like Abel, Jacobi, and Weierstrass to uncover a treasurehouse of results whose variety, aesthetic appeal, and capacity for arousing our astonishment have not since been equaled by research in any other area. But the circumstance that this theory can be applied to solve problems arising in many departments of science and engineering graces the topic with an additional aura and provides a powerful argument for including it in university courses for students who are expected to use mathematics as a tool for technological investigations in later life. Unfortunately, since the status of university staff is almost wholly determined by their effectiveness as research workers rather than as teachers, the content of undergraduate courses tends to reflect those academic research topics which are currently popular and bears little relationship to the future needs of students who are themselves not destined to become university teachers. Thus, having been comprehensively explored in the last century and being undoubtedly difficult .

Inhaltsverzeichnis

Frontmatter
Chapter 1. Theta Functions
Abstract
We shall introduce the theta functions by considering a specific heat conduction problem. The reader who is unfamiliar with the details of the following argument should return to this section in due course and, meanwhile, accept equations (1.1.8) and (1.1.12) as definitions of the theta functions θ 1 and θ 4 respectively.
Derek F. Lawden
Chapter 2. Jacobi’s Elliptic Functions
Abstract
The elliptic functions sn u, cn u, and dn u are defined as ratios of theta functions as below:
$$sn\;u = \frac{{{\theta _3}(0)}}{{{\theta _2}(0)}}\cdot \frac{{{\theta _1}(z)}}{{{\theta _4}(z)}},$$
(2.1.1)
$$cn\,u = \frac{{{\theta _4}(0)}}{{{\theta _2}(0)}}\cdot \frac{{{\theta _2}(z)}}{{{\theta _4}(z)}},$$
(2.1.2)
$$dn\;u = \frac{{{\theta _4}(0)}}{{{\theta _3}(0)}}\cdot \frac{{{\theta _3}(z)}}{{{\theta _4}(z)}},$$
(2.1.3)
where z = u 3 2 (0). sn u is read as “es en yew” or as “san yew”; cn u and dn u can similarly be read letter by letter or as “can u” and “dan u” respectively.
Derek F. Lawden
Chapter 3. Elliptic Integrals
Abstract
Throughout this chapter, the argument u and modulus k of all elliptic functions will be assumed real and, further, we suppose 0 < k < 1, unless stated otherwise.
Derek F. Lawden
Chapter 4. Geometrical Applications
Abstract
Taking an ellipse to have parametric equations
$$x = a\,\sin \theta ,\quad \in y = b\,\cos \theta ,$$
(4.1.1)
where a>b and the eccentric angle θ is measured from the minor axis, if s is the arc length parameter measured clockwise around the curve from the end B of the minor axis, then
$$d{s^2} = \sqrt {(d{x^2} + d{y^2})} = \sqrt {({a^2}{{\cos }^2}\theta + {b^2}{{\sin }^2}\theta )} d\theta = a\sqrt {(1 - {e^2}{{\sin }^2}\theta )} d\theta ,$$
(4.1.2)
where \(e = \sqrt {(1 - {b^2}/{a^2})} \) is the eccentricity. Thus, the length of arc from B to any point P where θ=Ø is given by
$$s = a\int_0^\phi {\sqrt {(1 - {e^2}{{\sin }^2}\theta )} } d\theta = aE(u,e),$$
(4.1.3)
where φ= am(u, e) or sn(u, e) = sin φ(vide equation (3.4.27)). Note that the modulus equals the eccentricity.
Derek F. Lawden
Chapter 5. Physical Applications
Abstract
Let l be the length of the suspension, g the gravitational acceleration, and m the mass of the bob. Then, if θ is the angle made by the string with the downward vertical and v is the velocity of the bob at any time t, its energy is conserved provided
$$\frac{1}{2}m{v^2} - mgl\cos \theta = con\tan t.$$
(5.1.1)
Derek F. Lawden
Chapter 6. Weierstrass’s Elliptic Function
Abstract
Given the complex parameter τ (with positive imaginary part), the quarter-periods K and iK′ of the Jacobian elliptic functions are determined by the equations (2.2.7) and (2.2.8); according to equation (2.2.3), r is precisely the ratio iK′/K of these quarter-periods. Thus it is possible to construct a set of Jacobi functions having a common pair of arbitrary periods 2ω1, 2ω3 in the following manner: First, choose the notation so that ω31 = τ has positive imaginary part (if this ratio is real, the elliptic functions cannot be defined (see section 8.1)). Secondly, construct Jacobian elliptic functions, sn u,etc., from theta functions with parameter τ. Thirdly, transform from the variable u to a new variable y by the equation u = 2Kv/ω 1. Clearly, the resulting functions of y will have periods 2ω1 and 2ω3. As proved in section 2.8, these functions will have exactly two simple poles in each of their primitive period parallelograms.
Derek F. Lawden
Chapter 7. Applications of the Weierstrass Functions
Abstract
Consider the transformation
$$z = p(w),$$
(7.1.1)
mapping a period parallelogram of p in the w-plane onto the z-plane. We shall suppose ω1 to be real and ω3 to be imaginary, so that the points e α=pα) all lie on the real axis in the z-plane (in the order e 3, e 2, e 1 from the left). Also, since p(w) is then real for real values of w, we shall have p(w*) = [p(w)]* (for the Taylor expansion of p about any point on the real axis must have real coefficients).
Derek F. Lawden
Chapter 8. Complex Variable Analysis
Abstract
As remarked in section 2.2, the general definition of an elliptic function is that it is a doubly periodic function, all of whose singularities (except at infinity) are poles. In section 2.3, we commented on the existence of primitive periods characterized by the property that any period is expressible as the sum of multiples of these primitive periods; we also distinguished between primitive periods and fundamental periods, a fundamental period being defined to be such that no submultiple is a period. We shall commence this chapter by proving the existence of primitive periods.
Derek F. Lawden
Chapter 9. Modular Transformations
Abstract
In sections 1.7 and 1.8, we studied the effect on the theta functions of transforming from a parameter τ to a parameter τ′, where τ′ = − 1/τ and τ′ = 2τ respectively. Then, in sections 2.6 and 3.9, it was shown that these transformations change the modulus of the Jacobian elliptic functions from k to \(k' = \sqrt {(1 - {k^2})} \) and from k to k 1 = (1− k′)/(1 + k′)respectively; the modulus transformation k = 1/k was also examined.
Derek F. Lawden
Backmatter
Metadaten
Titel
Elliptic Functions and Applications
verfasst von
Derek F. Lawden
Copyright-Jahr
1989
Verlag
Springer New York
Electronic ISBN
978-1-4757-3980-0
Print ISBN
978-1-4419-3090-3
DOI
https://doi.org/10.1007/978-1-4757-3980-0