Abstract
The main aim of this paper is to define and study of the Chebyshev matrix polynomials. An explicit representation, a three-term matrix recurrence relations for the Chebyshev matrix polynomials are given. These polynomials appear as finite series solutions of second order matrix differential equations. The expansion Chebyshev matrix polynomials in series of Hermite matrix polynomials and the Christoffel formula of summation are established.
Similar content being viewed by others
1 Introduction
Special functions, mathematical physics, and orthogonal polynomials are closely related [1, 6, 7, 20, 23, 24]. Special matrix functions appear in connection with statistics, mathematical physics, theoretical physics, Lie group theory, group representation theory, number theory and orthogonal matrix polynomials [9, 19]. Hermite and Laguerre matrix polynomials were introduced and studied in [2, 3, 5, 15, 16, 18, 21, 25–31]. Important connections between orthogonal matrix polynomials and matrix differential equations of the second order appear in [4, 10, 11, 22]. Jódar and Cortés [12] introduced and studied the hypergeometric matrix function and the hypergeometric matrix differential equation in and the explicit closed form general solution of it has been given in [13]. The reason of interest for this family of hypergeometric matrix functions is due to their intrinsic mathematical importance.
The primary goal of this paper is to consider a system of matrix polynomials, namely the Chebyshev matrix polynomials. The structure of this paper is organized as follows. In Sect. 2, a definition of Chebyshev matrix polynomials are given. Some differential recurrence relations, in particular Chebyshev’s matrix differential equation is established in Sect. 3. Expansion of the series and a connection between Chebyshev’s and Hermite’s matrix polynomials recently introduced in Section 4. Finally in Sect. 5, we obtain the Christoffel formula of summation.
Throughout this paper, for a matrix \(A\) in \(\mathbb {C}^{N \times N}\), its spectrum \(\sigma (A)\) denotes the set of all eigenvalues of \(A\). If \(A\) is a matrix in \(\mathbb {C}^{N\times N}\), its two-norm denoted by \(||A||_2\) and is defined by
where for a vector \(y\) in \(\mathbb {C}^{N}\), \(||y||_2\) denotes the usual Euclidean norm of \(y\), \(||y||_2=(y^Ty)^\frac{1}{2}\). \(I\) and \(O\) will denote the identity matrix and the null matrix in \(\mathbb {C}^{N\times N}\), respectively.
If \(f(z)\) and \(g(z)\) are holomorphic functions of the complex variable \(z\), which are defined in an open set \(\Omega \) of the complex plane, and if \(A\) is a matrix in \(\mathbb {C}^{N\times N}\) such that \(\sigma (A)\subset \Omega \), then from the properties of the matrix functional calculus [3, 15], it follows that
If \(A\) is a matrix with \(\sigma (A)\subset D_{0}\), then \(A^{\frac{1}{2}}=\sqrt{A}=\exp (\frac{1}{2}\log (A))\) denotes the image by \(z^\frac{1}{2}=\sqrt{z}=\exp (\frac{1}{2}\log (z))\) of the matrix functional calculus acting on the matrix \(A\). We say that \(A\) is a positive stable matrix [5, 14, 15] if
Throughout this study, consider the complex space \(\mathbb {C}^{N\times N}\) of all square complex matrices of common order \(N\). If \(A_{0}\), \(A_{1}\),...,\(A_{n}\) are elements of \(\mathbb {C}^{N\times N}\) and \(A_{n}\ne {0}\), then we call
a matrix polynomial of degree \(n\) in \(x\). Then from [20] it follows that
From (1.4), it is easy to find that
From the relation (1.5) of [1, 20], one obtains
The hypergeometric function \(F(a,b;c;z)\) has been given in the form [1, 20]
We will exploit the following relation due to
It has been seen by Defez and Jódar [3] that, for matrices \(A(k,n)\) and \(B(k,n)\) are matrices in \(\mathbb {C}^{N\times N}\) for \(n\ge 0\), \(k\ge 0\), the following relations are satisfied
and
Similarly, we can write
and
If \(A\) is a positive stable matrix in \(\mathbb {C}^{N\times N}\), then the \(n-{th}\) Hermite matrix polynomials was defined by [10]
For the sake of clarity, we recall that if \(A\) is a matrix in \(\mathbb {C}^{N\times N}\) satisfies the condition (1.2), than the expansion of \(x^nI\) in a series of Hermite matrix polynomials has been given in [3, 10] in the from
2 Definition of Chebyshev matrix polynomials
Let \(A\) be a positive stable matrix in \(\mathbb {C}^{N\times N}\) satisfying the condition (1.2). We define the Chebyshev matrix polynomials of the second kind by means of the relation
where \(I-xt\sqrt{2A}+t^2I\) is an invertible matrix and \(xt\sqrt{2A}-t^2I\) is an invertible matrix. Using (1.7) and (1.11), we have
By equating the coefficients of \(t^n\) in (2.1) and (2.2), we obtain an explicit representation of the Chebyshev matrix polynomials of the second kind in the form
Clearly, \(U_{n}(x,A)\) is a matrix polynomial of degree \(n\) in \(x\). Replacing \(x\) by \(-x\) and \(t\) by \(-t\) in (2.1), the left side does not exchange. Therefore
For \(x=0\), it follows
Also, by (1.7) one gets
Therefore, we have
The explicit representation (2.3) gives
where \(\prod _{n-2}\) is a matrix polynomial of degree \((n-2)\) in \(x\). Consequently, if \(D=\frac{d}{dx}\), then, it follows that
3 Differential recurrence relations
In this section, the three terms recurrence relation and differential recurrence relations are carried out on the Chebyshev matrix polynomials.
Differentiating (2.1) with respect to \(x\) and \(t\) respectively
and
So that the matrix function \(F\) satisfies the partial matrix differential equation
Therefore, by (2.1) we get
Since \(DU_{0}(x,A)=\mathbf 0 \) and for \(n\ge 1\), then we obtain the differential recurrence relation
From (3.1) and (3.2) with the aid of (2.1), we get
and
Note that \(I-t^2I-t(x\sqrt{2A}-2tI)=I-xt\sqrt{2A}+t^2I\). Thus by multiplying (3.4) by \(I-t^2I\) and (3.5) by \(t\) and subtracting (3.5) from (3.4), we obtain
From (3.3) and (3.6), one gets
Substituting \(n-1\) for \(n\) in (3.7) and putting the resulting expression for \(DU_{n-1}(x,A)\) into (3.3), gives
Now, by multiplying (3.3) by \(((x\sqrt{2A})^2-4I)\) and substituting for \(((x\sqrt{2A})^2-4I)DU_{n}(x,A)\) and \(((x\sqrt{2A})^2-4I)DU_{n-1}(x,A)\) from (3.8) to obtain the three terms recurrence relation in the form
Substituting for \(n\) in (3.6) the values \(n-1\), \(n-2\), ...,\(2\), \(1\), \(0\) and adding we obtain (\(U_{0}(x,A)=I\), \(U'_{0}(x,A)=\mathbf 0 \), \(U'_{1}(x,A)=\sqrt{2A}\))
Formulas (3.3), (3.6), (3.7), (3.8) (3.9) and (3.10) are called the recurrence formulas for Chebyshev matrix polynomials. The first few Chebyshev matrix polynomials are listed here,
and
We conclude this section introducing the Chebyshev’s matrix differential equation as follows
In (3.7), replace \(n\) by \(n-1\) and differentiate with respect to \(x\) to find
Also, by differentiating (3.3) with respect to \(x\), we have
From (3.3) and (3.12) by putting \(DU_{n-1}(x,A)\) and \(D^2U_{n}(x,A)\) into (3.11) and rearrangement terms, we obtain the Chebyshev’s matrix differential equation in the form
In the following, we can expand the Chebyshev matrix polynomials in series of Hermite matrix polynomials.
4 Expanding of Chebyshev matrix polynomials in series of Hermite matrix polynomials
Employing (2.1) and (1.15) with the aid of (1.11), we consider the series
Since the matrix \(A\) commutes with itself, then we can write (4.1) in the form
Thus
By using (1.11) the expression (4.2) becomes
this, by using (1.10), yields,
Since
then by using (1.5) and (1.9), it follows
Therefore, by identification of coefficient of \(t^n\), we obtain an expansion of Chebyshev matrix polynomials as a series of Hermite matrix polynomials in the form
In the following, we obtain recurrence formula of summation for the Chebyshev matrix polynomials as follows.
5 The Christoffel formula of summation
The pure recurrence relation of Chebyshev matrix polynomials (3.9), substituting \(n+1\) for \(n\) gives
We wish to prove the identity
Form (5.1), substituting \(i\) for \(n\) and multiplying by
Interchanging \(x\) and \(y\)
subtracting
Setting \(i=0,1,2,\ldots ,n\), we obtain
and
whence (5.2) follows by addition. Hence the Christoffel formula (5.2) is established.
Finally, the Hermite matrix polynomials of two variables \(H_{n}(x,\frac{1}{t},A)\) [2] will be exploited here to define a matrix version of Chebyshev polynomials of the second kind by means of the integral transform
In a similar way, we define the Chebyshev matrix polynomials of the first kind [4] as follows
We obtain the fundamental recurrence relations
and
Further examples (orthogonal matrix polynomials) proving the usefulness of the present method (integral transform) can be easily worked out, but are not reported here for conciseness.
6 Open problem
One can use the same class of new differential and integral operators for the new matrix polynomials. Hence, new results and further applications can be obtained. Further applications will be discussed in a forthcoming paper.
References
Andrews, L.C.: Special Functions for Engineers and Applied Mathematicians. MacMillan, New York (1985)
Batahan, R.S.: A new extension of Hermite matrix polynomials and its applications. Linear Algebra Appl. 419, 82–92 (2006)
Defez, E., Jódar, L.: Some applications of the Hermite matrix polynomials series expansions. J. Comput. Appl. Math. 99, 105–117 (1998)
Defez, E., Jódar, L.: Chebyshev matrix polynomials and second order matrix differential equations. Utilitas Math. 61, 107–123 (2002)
Defez, E., Hervás, A., Jódar, L., Law, A.: Bounding Hermite matrix polynomials. Math. Comput. Modell. 40, 117–125 (2004)
Durán, A.J.: Markov’s Theorem for orthogonal matrix polynomials. Can. J. Math. 48, 1180–1195 (1996)
Durán, A.J., Lopez-Rodriguez, P.: Orthogonal matrix polynomials: zeros and Blumenthal Theorem. J. Approx. Theory 84, 96–118 (1996)
Gohberg, I., Lancaster, P., Rodman, L.: Matrix Polynomials. Academic Press, New York (1982)
James, A.T.: Special functions of matrix and single argument in statistics. In: Askey, R.A. (ed.) Theory and Applications of Special Functions, pp. 497–520. Academic Press, New York (1975)
Jódar, L., Company, R.: Hermite matrix polynomials and second order matrix differential equations. J. Approx. Theory Appl. 12, 20–30 (1996)
Jódar, L., Company, R., Navarro, E.: Laguerre matrix polynomials and system of second-order differential equations. Appl. Numer. Math. 15, 53–63 (1994)
Jódar, L., Cortés, J.C.: On the hypergeometric matrix function. J. Comput. Appl. Math. 99, 205–217 (1998)
Jódar, L., Cortés, J.C.: Closed form general solution of the hypergeometric matrix differential equation. Math. Comput. Model. 32, 1017–1028 (2000)
Jódar, L., Defez, E.: A connection between Laguerre’s and Hermite’s matrix polynomials. Appl. Math. Lett. 11, 13–17 (1998)
Jódar, L., Defez, E.: On Hermite matrix polynomials and Hermite matrix function. J. Approx. Theory Appl. 14, 36–48 (1998)
Jódar, L., Sastre, J.: The growth of Laguerre matrix polynomials on bounded intervals. Appl. Math. Lett. 13, 21–26 (2000)
Mason, J.L., Handscomb, D.C.: Chebyshev Polynomials. Chapman and Hall/CRC, New York (2003)
Metwally, M.S., Mohamed, M.T., Shehata, A.: On Hermite-Hermite matrix polynomials. Math. Bohemica 133, 421–434 (2008)
Muirhead, R.J.: Systems of partial differential equations for hypergeometric functions of matrix argument. Ann. Math. Stat. 41, 991–1001 (1970)
Rainville, E.D.: Special Functions. The Macmillan Company, New York (1960)
Sayyed, K.A.M., Metwally, M.S., Batahan, R.S.: On generalized Hermite matrix polynomials. Electron. J. Linear Algebra 10, 272–279 (2003)
Sayyed, K.A.M., Metwally, M.S., Batahan, R.S.: Gegenbauer matrix polynomials and second order matrix differential equations. Divulgaciones Mate. 12, 101–115 (2004)
Sinap, A., Van Assche, W.: Orthogonal matrix polynomials and applications. J. Comput. Appl. Math. 66, 27–52 (1996)
Terras, A.: Special functions for the symmetric space of positive matrices. SIAM J. Math. Anal. 16, 620–640 (1985)
Sayyed, K.A.M., Metwally, M.S., Mohamed, M.T.: Certain hypergeometric matrix function. Sci. Math. Jpn. 69, 315–321 (2009)
Shehata, A.: A study of some special functions and polynomials of complex variables. Ph.D. Thesis, Assiut University, Assiut, Egypt (2009)
Shehata, A.: On Tricomi and Hermite-Tricomi matrix functions of complex variable. Commun. Math. Appli. 2(2–3), 97–109 (2011)
Shehata, A.: A new extension of Hermite-Hermite matrix polynomials and their properties. Thai J. Math. 10(2), 433–444 (2012)
Shehata, A.: A new extension of Gegenbauer matrix polynomials and their properties. Bull. Inter. Math. Virtual Inst. 2, 29–42 (2012)
Shehata, A.: On pseudo Legendre matrix polynomials. Inter. J. Math. Sci. Eng. Appl. (IJMSEA) 6(VI), 251–258 (2012)
Upadhyaya, L.M., Shehata, A.: On Legendre matrix polynomials and its applications. Inter. Tran. Math. Sci. Comput. (ITMSC) 4(2), 291–310 (2011)
Acknowledgments
(1) The Author (A. Shehata) expresses his sincere appreciation to Shimaa Ibrahim Moustafa Abdal-Rahman, (Department of Mathematics, Faculty of Science, Assiut University, Assiut 71516, Egypt) for his kind interest, encouragements, help, suggestions, comments and the investigations for this series of papers. (2) The authors would like to thank the referees for their valuable comments and suggestions which have led to the better presentation of the paper.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.
About this article
Cite this article
Metwally, M.S., Mohamed, M.T. & Shehata, A. On Chebyshev matrix polynomials, matrix differential equations and their properties. Afr. Mat. 26, 1037–1047 (2015). https://doi.org/10.1007/s13370-014-0262-y
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s13370-014-0262-y
Keywords
- Hermite matrix polynomials
- Chebyshev matrix polynomials
- Matrix recurrence relation
- Matrix differential equations
- Christoffel formula