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In this paper, we mainly consider finding an explicit formula for the inverse of a pentadiagonal Toeplitz matrix. For that purpose, we first factorize the modified form of a pentadiagonal Toeplitz matrix by two tridiagonal Toeplitz matrices, and then use the.Sherman–Morrison–Woodbury inversion formula. As a result, an explicit inverse of a pentadiagonal Toeplitz matrix is obtained under certain assumptions. And numerical experiments are given to show the effectiveness of our results.
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Journal of Computational and Applied Mathematics 278 (2015) 12–18
Contents lists available at ScienceDirect
Journal of Computational and Applied
Mathematics
journal homepage: www.elsevier.com/locate/cam
An explicit formula for the inverse of a pentadiagonal
Toeplitz matrix
Chaojie Wang, Hongyi Li, Di Zhao
∗
LMIB, School of Mathematics and System Science, Beihang University, Beijing, 100191, PR China
a r t i c l e i n f o
Article history:
Received 29 December 2013
Received in revised form 26 May 2014
Keywords:
Inverse
Pentadiagonal matrix
Toeplitz matrix
Factorization
Sherman–Morrison–Woodbury inversion
a b s t r a c t
In this paper, we mainly consider finding an explicit formula for the inverse of a pen-
tadiagonal Toeplitz matrix. For that purpose, we first factorize the modified form of a
pentadiagonal Toeplitz matrix by two tridiagonal Toeplitz matrices, and then use the
Sherman–Morrison–Woodbury inversion formula. As a result, an explicit inverse of a pen-
tadiagonal Toeplitz matrix is obtained under certain assumptions. And numerical experi-
ments are given to show the effectiveness of our results.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
The n-by-n pentadiagonal Toeplitz matrix takes the form
A =
x y v
z x y
.
.
.
w z x
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
v
.
.
.
.
.
.
.
.
.
y
w z x
. (1.1)
Pentadiagonal Toeplitz matrices often occur when solving partial differential equations numerically using finite
difference method, finite element method and spectral method, and could be applied to the mathematical representation
of high dimensional, nonlinear electromagnetic interference signals [1–7]. Pentadiagonal matrices are a certain class of
special matrices, and other common types of special matrices are Jordan, Frobenius, generalized Vandermonde, Hermite,
centrosymmetric, and arrowhead matrices [8–12]. Usually, after the original partial differential equations are processed
with these numerical methods, we need to solve the pentadiagonal Toeplitz systems of linear equations for obtaining the
numerical solutions of the original partial differential equations. Thus, the inversion of pentadiagonal Toeplitz matrices is
necessary to solve the partial differential equations in these cases.
Recently, J. Jia, T. Sogabe and M. El-Mikkawy have proposed an explicit inverse of the tridiagonal Toeplitz matrix which is
strictly row diagonally dominant [13]. However, this result cannot be generalized to the case of the pentadiagonal Toeplitz
matrix directly. This motivates us to investigate whether an explicit inverse of the pentadiagonal Toeplitz matrix also exists.
∗
Corresponding author.
E-mail addresses: zdbuaa@163.com, hylbuaa@163.com (D. Zhao).
http://dx.doi.org/10.1016/j.cam.2014.08.010
0377-0427/© 2014 Elsevier B.V. All rights reserved.
C. Wang et al. / Journal of Computational and Applied Mathematics 278 (2015) 12–18 13
Based on the results presented in [13], we derive an explicit formula for the inverse of the pentadiagonal Toeplitz ma-
trix under some assumptions by using the Sherman–Morrison–Woodbury inversion formula and the factorization of the
modified pentadiagonal Toeplitz matrices [14].
The remainder of this paper is organized as follows: in Section 2, we perform a comparison with other methods. In
Section 3, a method for obtaining the inverse of a pentadiagonal Toeplitz matrix is given. In Section 4, a numerical example
is provided to show the effectiveness of our results. Finally, we present some concluding remarks in Section 5.
2. Comparison with other methods
In recent years, many researchers have studied the inversion of the pentadiagonal Toeplitz matrix or related matrices:
• In [15,16], the authors proposed two explicit formulas for the inverse of general Toeplitz matrices, respectively. These
two methods could be directly applied to inverting the pentadiagonal Toeplitz matrix, but they could not make full use
of the sparse structure of the pentadiagonal Toeplitz matrix.
• [17] gave a method to obtain the inverse of a general pentadiagonal matrix which was not specific to the pentadiagonal
Toeplitz matrix and required general Doolittle factorization.
• [18] presented a numerical method for computing the inverse of the pentadiagonal Toeplitz matrix that involves solving
a system of linear equations.
In summary, all the above methods are not very efficient for the inversion of the pentadiagonal Toeplitz matrix. This
motivates us to find a better method for computing the inverse of the pentadiagonal Toeplitz matrix.
3. Main results
In this section, we derive an explicit formula for computing the inverse of a pentadiagonal Toeplitz matrix.
3.1. The factorization of the modified pentadiagonal Toeplitz matrix by tridiagonal Toeplitz matrices
It is easy to prove that the product of any two tridiagonal Toeplitz matrices is not a pentadiagonal Toeplitz matrix because
the first and last elements in the principle diagonal are different from the other ones [19,20]. Thus, it is necessary to consider
the factorization of a pentadiagonal Toeplitz matrix modified in the first and the last element of the principle diagonal.
Let the modified form of A be an n-by-n pentadiagonal matrix as the following
A
M
=
x − α y v
z x y
.
.
.
w z x
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
v
.
.
.
.
.
.
.
.
.
y
w z x − β
. (3.1)
The real tridiagonal Toeplitz matrix of size n is given by
T =
b c
a b
.
.
.
.
.
.
.
.
.
c
a b
. (3.2)
Denote it by
T = trid
n
[a, b, c].
Factorize A
M
by two tridiagonal Toeplitz matrices as
A
M
= T
1
T
2
(3.3)
where
T
1
= trid
n
[a
1
, b
1
, c
1
], T
2
= trid
n
[a
2
, b
2
, c
2
]. (3.4)
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