Discrete Dynamics in Nature and Society

Volume 2014 (2014), Article ID 568129, 6 pages

http://dx.doi.org/10.1155/2014/568129

Research Article

Analytic Continuation of Euler Polynomials and the Euler Zeta Function

C. S. Ryoo

Department of Mathematics, Hannam University, Daejeon 306-791, Republic of Korea

Received 10 January 2014; Accepted 10 March 2014; Published 3 April 2014

Academic Editor: Binggen Zhang

Copyright © 2014 C. S. Ryoo. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

We study that the Euler numbers and Euler polynomials are analytically continued to and . We investigate the new concept of dynamics of the zeros of analytica continued polynomials. Finally, we observe an interesting phenomenon of “scattering” of the zeros of .

1. Introduction

Throughout this paper, , , and will denote the ring of integers, the field of real numbers, and the complex numbers, respectively. Recently, many mathematicians have studied different kinds of the Euler, Bernoulli, and Genocchi numbers and polynomials (see [1–19]). The computing environment would make more and more rapid progress and there has been increasing interest in solving mathematical problems with the aid of computers. By using software, mathematicians can explore concepts much more easily than in the past. The ability to create and manipulate figures on the computer screen enables mathematicians to quickly visualize and produce many problems, examine properties of the figures, look for patterns, and make conjectures. This capability is especially exciting because these steps are essential for most mathematicians to truly understand even basic concept. Numerical experiments of Bernoulli polynomials, Euler polynomials, and Genocchi polynomials have been the subject of extensive study in recent years and much progress has been made both mathematically and computationally. Using computer, a realistic study for Euler polynomials is very interesting. It is the aim of this paper to observe an interesting phenomenon of “scattering” of the zeros of the Euler polynomials in complex plane. First, we introduce the Euler numbers and Euler polynomials. As a well-known definition, the Euler numbers are defined by

Here is the list of the first Euler numbers:

The Euler polynomials are defined by the generating function:

where we use the technique method notation by replacing by symbolically.

Because

an important relation follows:

Then, it is easy to deduce that are polynomials of degree . Here is the list of the first Euler polynomials:

2. Generating Euler Polynomials and Numbers

Since

we have the following theorem.

Theorem 1. For , one has

Definition 2. For with , define the Euler zeta function by

see [7–10].

Notice that the Euler zeta function can be analytically continued to the whole complex plane, and these zeta functions have the values of the Euler numbers at negative integers. That is, Euler numbers are related to the Euler zeta function as

Definition 3. We define the Hurwitz zeta function for with and with by

see [3, 7–10, 12].

Euler polynomials are related to the Hurwitz zeta function as

We now consider the function as the analytic continuation of Euler numbers. From the above analytic continuation of Euler numbers, we consider

All the Euler numbers agree with , the analytic continuation of Euler numbers evaluated at (see Figure 1),

Figure 1: The curve runs through the points of all except .

In fact, we can express in terms of , the derivative of ,

From relation (16), we can define the other analytic continued half of Euler numbers as

By (17), we have

The curve runs through the points and grows ~−2 asymptotically as (see Figure 2).

Figure 2: The curve runs through the points .

3. Analytic Continuation of Euler Polynomials

Looking back at (1) and (3), we can see that the sign convention of was actually arbitrary. Equation (15) suggests that consistent definition of Euler numbers should really have been

which only changes the sign in the conventional definition of the only nonzero even Euler numbers, , from to .

By using Cauchy product, we have

For consistency with the redefinition of in (19), Euler polynomials should be analogously redefined as

The analytic continuation can be then obtained as

where gives the integer part of , and so gives the fractional part.

By (22), we obtain analytic continuation of Euler polynomials:

By using (23), we plot the deformation of the curve into the curve of via the real analytic continuation , , (see Figure 3).

Figure 3: The curve of , , .

Next, we investigate the beautiful zeros of the by using a computer. We plot the zeros of for and (Figure 4).

(a)

(b)

(c)

(d)

Figure 4: Zeros of for .

In Figure 4(a), we choose . In Figure 4(b), we choose . In Figure 4(c), we choose . In Figure 4(d), we choose .

Since

we obtain

Hence, we have the following theorem.

Theorem 4. If , then , for .

The question is, what happens with the reflexive symmetry (25) when one considers Euler polynomials? Prove that , , has reflection symmetry in addition to the usual reflection symmetry analytic complex functions. However, we observe that , , does not have reflection symmetry analytic complex functions (Figure 4).

Our numerical results for approximate solutions of real zeros of are displayed. We observe a remarkably regular structure of the complex roots of Euler polynomials. We hope to verify a remarkably regular structure of the complex roots of Euler polynomials (Table 1). Next, we calculated an approximate solution satisfying , . The results are given in Table 2.

Table 1: Numbers of real and complex zeros of .

Real zeros
Complex zeros

1.5
2
0

2.5
3
0

3.5
4
0

4.5
5
0

5.5
2
4

6.5
3
4

7.5
4
4

8.5
5
4

9
5
4

9.6
6
4

9.8
6
4

10
6
4

Table 2: Approximate solutions of , .

6

6.5

7

7.5

8

8.5

9

9.6

9.8

10

Euler polynomials are polynomials of degree . Thus, has zeros and has zeros. When discrete is analytically continued to continuous parameter , it naturally leads to the following question: how does , the analytic continuation of , pick up an additional zero as increases continuously by one?

This introduces the exciting concept of the dynamics of the zeros of analytic continued polynomials, the idea of looking at how the zeros move about in the complex plane as we vary the parameter . For more studies and results in this subject you may see [11, 14–16].

Conflict of Interests

The author declares that there is no conflict of interests regarding the publication of this paper.

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