Research Article | Open Access

# Further Results on the Dilogarithm Integral

**Academic Editor:**Ch Tsitouras

#### Abstract

The dilogarithm integral Li() and its associated functions and are defined as locally summable functions on the real line. Some convolutions and neutrix convolutions of these functions and other functions are then found.

#### 1. Introduction

The dilogarithm integral is defined by (see [1]). More generally, we have for .

The associated functions and are defined by where denotes Heaviside's function.

Next, we define the distribution by and its associated distributions and are defined by

The classical definition of the convolution product of two functions and is as follows.

*Definition 1.1. **Let ** and ** be functions. Then the convolution ** is defined by *
for all points for which the integral exist.

It follows easily from the definition that if exists then exists and and if and exists, then Definition 1.1 can be extended to define the convolution of two distributions and in with the following definition; see Gel'fand and Shilov [2].

*Definition 1.2. **Let ** and ** be distributions in **. Then the convolution ** is defined by the equation *
for arbitrary in , provided and satisfy either of the following conditions:(a)either or has bounded support,(b)the supports of and are bounded on the same side.

It follows that if the convolution exists by this definition then (1.7) and (1.8) are satisfied.

In order to extend Definition 1.2 to distributions which do not satisfy conditions (a) or (b), let be a function in , see [3], satisfying the conditions:

(i) ,

(ii) ,

(iii) ,

(iv) .

The function is then defined by for .

The following definition of the noncommutative neutrix convolution was given in [4].

*Definition 1.3. **Let ** and ** be distributions in **, and let ** for **. Then the noncommutative neutrix convolution ** is defined as the neutrix limit of the sequence **, provided the limit ** exists in the sense that *
for all in , where is the neutrix, see van der Corput [5], having domain the positive reals and range the real numbers, with negligible functions finite linear sums of the functions
and all functions which converge to zero in the normal sense as tends to infinity.

In particular, if
exists, we say that the non-commutative convolution exists.

It is easily seen that any results proved with the original definition of the convolution hold with the new definition of the neutrix convolution. Note also that because of the lack of symmetry in the definition of the neutrix convolution is in general non-commutative.

The following results proved in [4] hold, first showing that the neutrix convolution is a generalization of the convolution.

Theorem 1.4. *Let and be distributions in , satisfying either condition (a) or condition (b) of Gel'fand and Shilov's definition. Then the neutrix convolution exists and
*

Theorem 1.5. *Let and be distributions in and suppose that the neutrix convolution exists. Then the neutrix convolution exists and
*

Note however that is not necessarily equal to but we do have the following theorem.

Theorem 1.6. *Let and be distributions in and suppose that the neutrix convolution exists. If exists and equals for all in , then exists and
*

#### 2. Main Result

We define the function by for and . In particular, we define the function by for .

The following theorem was proved in [6].

Theorem 2.1. *The convolutions **
for and
**
for .*

We now prove the following generalization of Theorem 2.1.

Theorem 2.2. *The convolutions and exist and
**
for , and
**
for .*

*Proof. *It is obvious that if .

When , we have
proving (2.5).

Next, using (1.8) and (2.5), we have
and (2.6) follows.

Corollary 2.3. *The convolutions and exist and
**
for , and
**
for .*

*Proof. *Equations (2.9) and (2.10) are obtained applying a similar procedure as used in obtaining (2.5) and (2.6).

The next two theorems were proved in [6] and to prove it, our set of negligible functions was extended to include finite linear sums of the functions for and .

Theorem 2.4. *The convolution exists and
**
for . *

Theorem 2.5. *The convolution exists and
**
for .*

Before proving some further results, we need the following lemma.

Lemma 2.6. *If for , then
*

*Proof. *Because
when , we have
and (2.13) follows.

We now prove the following generalization of Theorems 2.4 and 2.5.

Theorem 2.7. *The neutrix convolution exists when and
**
for .*

*Proof. *We put . Then the convolution exists by Definition 1.1 and
where
Thus, using Lemma 2.6, we have

Further, it is easily seen that
and (2.16) follows from (2.17), (2.19), and (2.20), proving the theorem.

Theorem 2.8. *The neutrix convolution exists when and
**
for .*

*Proof. *Using Theorems 1.5 and 1.6, we have
where, on integration by parts, we have

It is clear that
It now follows from (2.23) and (2.24) that
Equation (2.21) now follows directly from (2.16) and (2.22), proving the theorem.

Corollary 2.9. *The neutrix convolutions and exist when and
**
for *

*Proof. *Equations (2.26) are obtained applying a similar procedure as used in obtaining (2.16) and (2.21).

Corollary 2.10. *The neutrix convolutions and exist when and
**
for .*

*Proof. *Since the neutrix convolution product is distributive with respect to addition, we have
and (2.27) follows from (2.16) and (2.5). Equation (27) is obtained applying similar procedure as in the case of (2.27).

Corollary 2.11. *The neutrix convolutions and exist when and
**
for *

*Proof. *Equation (2.29) follows from (2.21) and (2.6). Equation (29) is obtained applying similar procedure as in the case of (2.29).

#### Acknowledgment

This research was supported by FEIT, University of Ss. Cyril and Methodius in Skopje, Republic of Macedonia, Project no. 08-3619/8.

#### References

- M. Abramowitz and I. A. Stegun,
*Handbook of Mathematical Functions with Formulas, Graphs and Mathematical Tables*, Dover, New York, NY, USA, 9th edition, 1972. - I. M. Gel'fand and G. E. Shilov,
*Generalized Functions*, vol. 1, chapter 1, Academic Press, New York, NY, USA, 1964. - D. S. Jones, “The convolution of generalized functions,”
*The Quarterly Journal of Mathematics*, vol. 24, pp. 145–163, 1973. View at: Publisher Site | Google Scholar | Zentralblatt MATH - B. Fisher, “Neutrices and the convolution of distributions,”
*Univerzitet u Novom Sadu. Zbornik Radova Prirodno-Matematičkog Fakulteta. Serija za Matemati*, vol. 17, no. 1, pp. 119–135, 1987. View at: Google Scholar - J. G. van der Corput, “Introduction to the neutrix calculus,”
*Journal d'Analyse Mathématique*, vol. 7, pp. 291–398, 1959. View at: Publisher Site | Google Scholar - B. Jolevska-Tuneska, B. Fisher, and E. Özçağ, “On the dilogarithm integral,”
*International Journal of Applied Mathematics*, vol. 24, no. 3, pp. 361–369, 2011. View at: Google Scholar

#### Copyright

Copyright © 2011 Biljana Jolevska-Tuneska and Brian Fisher. 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.