Keywords: function of two variables, Bessel polynomials, MellinBarnes type integral, Timedomain synthesis problem,Hfunction of two variables
Turkish Journal of Analysis and Number Theory, 2014 2 (4),
pp 130133.
DOI: 10.12691/tjant245
Received July 01, 2014; Revised August 01, 2014; Accepted August 15, 2014
Copyright © 2013 Science and Education Publishing. All Rights Reserved.
1. Introduction
The object of this paper is to evaluate an integral involving Bessel polynomials and the function of two variables due to Singh and Mandia ^{[8]}, and to apply it in obtaining a particular solution of the classical problem known as the ‘timedomain synthesis problem’, occurring in the electric network theory. On specializing the parameters, the function of two variables may be reduced to almost all elementary functions and special functions appearing in applied Mathematics Erdelyi, A. et. al. (^{[2]}, p.215222). The special solution derived in the paper is of general character and hence may encompass several cases of interest.
The function of two variables will be defined and represented by Singh and Mandia ^{[8]} in the following manner:
 (1.1) 
Where
 (1.2) 
 (1.3) 
 (1.4) 
Where and are not equal to zero (real or complex), and an empty product is interpreted as unity are nonnegative integers such that . All the are complex parameters. (not all zero simultaneously), similarly (not all zero simultaneously). The exponents can take on nonnegative values.
The contour is in plane and runs from to . The poles of lie to the right and the poles of to the left of the contour. For not an integer, the poles of gamma functions of the numerator in (1.3) are converted to the branch points.
The contour is in plane and runs from to . The poles of lie to the right and the poles of to the left of the contour. For not an integer, the poles of gamma functions of the numerator in (1.4) are converted to the branch points.
The functions defined in (1.1) is an analytic function of and , if
 (1.5) 
 (1.6) 
The integral in (1.1) converges under the following set of conditions:
 (1.7) 
 (1.8) 
 (1.9) 
The behavior of the function of two variables for small values of follows as:
 (1.10) 
Where
 (1.11) 
For large value of ,
 (1.12) 
Where
 (1.13) 
Provided that and .
If we take in (1.1), the function of two variables reduces to function of two variables due to ^{[7]}.
The following results are needed in the analysis that follows:
Bessel polynomials are defined as
 (1.14) 
Orthogonality property of Bessel polynomials is derived by Exton (^{[4]}, p.215, (14)):
 (1.15) 
Where .
The integral defined by Bajpai et.al. ^{[1]} is also required:
 (1.16) 
Where .
2. Integral
The integral to be evaluated is
 (2.1) 
Where
For , and conditions (1.7), (1.8) and (1.9) are also satisfied.
Proof: To establish (2.1), express the function of two variables in its integrand as a MellinBarnes type integral (1.1) and interchange the order of integration which is permissible due to the absolute convergence of the integrals involved in the process, we obtain
Now evaluating the inner integral with the help of (1.16), it becomes
Which on applying (1.1), yields the desired result (2.1).
Special Case: If we take in (1.1), the function of two variables reduces to function of two variables due to ^{[7]}, and we get
 (2.2) 
Provided all condition are satisfied given in (2.1).
3. Solution of the TimeDomain Synthesis Problem of Signals
The classical timedomain synthesis problem occurring in electric network theory is as follows (^{[4]}, p. 139):
Given an electrical signal described by a real valued conventional function on , construct an electrical network consisting of finite number of components and which are all fixed, linear and positive, such that output of , resulting from a deltafunction approximates on in some sense.
In order to obtain a solution of this problem, we expand the function into a convergent series:
 (3.1) 
Or realvalued function . Let every partial sum
 (3.2) 
Possesses the two properties
(i) for
(ii) The Laplace transform 0f is a rational function having a zero as and all its poles in the lefthand plane, except possibly for a simple pole at the origin.
After choosing in (3.2) sufficiently large whatever approximation criterion is being used, an orthogonal series expansion may be employed. The Bessel polynomial transformation and (1.15) yields as immediate solution in the following form:
Where
 (3.3) 
Where .
The function is continuous and of bounded variation in the open interval.
4. Particular Solution of the Problem
The particular solution of the problem is:
 (4.1) 
Where and result (1.7), (1.8) and (1.9) are also holds.
Proof: Let us consider
 (4.2) 
Equation (4.2) is valid, since is continuous and of bounded variation in the open interval .
Multiplying both sides of (4.2) by and integrating with respect to fromto , we get
Now using (2.1) and (1.15), we obtain
 (4.3) 
On account of the most general character of the result (4.2) due to presence of the function of two variables, numerous special cases can be derived but further sake of brevity those are not presented here.
References
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 In article  

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 In article  

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 In article  

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