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HomeMatlabWhat Is a Toeplitz Matrix? – Nick Higham

What Is a Toeplitz Matrix? – Nick Higham


Tinmathbb{C}^{ntimes n} is a Toeplitz matrix if t_{ij} = t_{i-j} for 2n-1 parameters t_{1-n},dots,t_{n-1}. A Toeplitz matrix has fixed diagonals. For n = 4:

notag   T = begin{bmatrix} t_0 & t_{-1} & t_{-2} & t_{-3}                t_1 & t_0    & t_{-1} & t_{-2}                t_2 & t_1    & t_0    & t_{-1}                t_3 & t_2    & t_1    & t_0 end{bmatrix}.

Toeplitz matrices come up in numerous issues, together with evaluation of time sequence, discretization of fixed coefficient differential equations, and discretization of convolution equations int a(t-s)x(s),mathrm{d} s = b(t).

Since a Toeplitz matrix relies on simply 2n-1 parameters it’s affordable to anticipate {that a} linear system Tx = b might be solved in lower than the O(n^3) flops that will be required by LU factorization. Certainly strategies can be found that require solely O(n^2) flops; see Golub and Van Mortgage (2013) for particulars.

Higher triangular Toeplitz matrices might be written within the type

notag T = sum_{j=1}^n t_{1-j} N^{j-1}, quad      N = begin{bmatrix} 0 & 1      &        &                        & 0      & ddots &                        &        & ddots &   1                       &        &        &   0 end{bmatrix},

the place N is higher bidiagonal with a superdiagonal of ones and N^n = 0. It follows that the product of two higher triangular Toeplitz matrices is once more higher triangular Toeplitz, higher triangular Toeplitz matrices commute, and T^{-1} can also be an higher triangular Toeplitz matrix (assuming t_0 is nonzero, in order that T is nonsingular).

Tridiagonal Toeplitz matrices come up regularly:

notag  T(c,d,e) = begin{bmatrix}                      d   & e      &        &                           c & d      & ddots &                             & ddots & ddots & e                           &        & c      & d                end{bmatrix} inmathbb{C}^{ntimes n}.

The eigenvalues of T(c,d,e) are

notag         d + 2 (ce)^{1/2} cosbiggl( displaystylefrac{k pi}{n+1} biggr),         quad k = 1:n.

The Kac–Murdock–Szegö matrix is the symmetric Toeplitz matrix

notag A(rho) = begin{bmatrix}    1          & rho       & rho^2 & dots  & rho^{n-1}     rho       & 1          & rho   & dots  & rho^{n-2}     rho^2     & rho       & 1      & ddots & vdots         vdots     & vdots     & ddots & ddots & rho           rho^{n-1} & rho^{n-2} & dots  & rho   & 1 end{bmatrix}.

It has a variety of fascinating properties.

In MATLAB, a Toeplitz matrix might be constructed utilizing toeplitz(c,r), which produces the matrix with first column c and first row r. Instance:

>> n = 5; A = toeplitz(1:n,[1 -2:-1:-n])
A =
     1    -2    -3    -4    -5
     2     1    -2    -3    -4
     3     2     1    -2    -3
     4     3     2     1    -2
     5     4     3     2     1

References

  • Gene Golub and Charles F. Van Mortgage, Matrix Computations, fourth version, Johns Hopkins College Press, Baltimore, MD, USA, 2013. Part 4.7.

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