Mathematics Commons^™

Bulk Spectrum And K-Theory For Infinite-Area Topological Quasicrystals [Dataset], Terry A. Loring

Math and Statistics Datasets

Archived here are files, data and program files, that are supplementary the following article, expected to be published in 2019:

* Terry A. Loring. Bulk Spectrum and K-theory for Infinite-Area Topological Quascrystal. Journal of Mathematical Physics, (2019 est.).

The files, in Matlab format, allow the user to create approximate eigenvalues for a topological Hamilontian on a round patch of a quasicrystal. The data files describe pathes of the Ammann-Bennkeer tiling. One of the data files is really large. Read the file README.txt first (available via the main download button), so see if you can avoid downloading the largest file.

Recommended …

K-Theory And Pseudospectra For Topological Insulators [Dataset], Terry A. Loring

Math and Statistics Datasets

We derive formulas and algorithms for Kitaev's invariants in the periodic table for topological insulators and superconductors for finite disordered systems on lattices with boundaries. We find that K-theory arises as an obstruction to perturbing approximately compatible observables into compatible observables. We derive formulas in all symmetry classes up to dimension two, and in one symmetry class in dimension three, that can be computed with sparse matrix algorithms. We present algorithms in two symmetry classes in 2D and one in 3D and provide illustrative studies regarding how these algorithms can detect the scaling properties of phase transitions.

Quantitative K-Theory And Spin Chern Numbers [Dataset], Terry A. Loring

Math and Statistics Datasets

We examine the various indices defined on pairs of almost commuting unitary matrices that can detect pairs that are far from commuting pairs. We do this is two symmetry classes, that of general unitary matrices and that of self-dual matrices, with an emphasis on quantitative results. We determine what values of the norm of the commutator guarantee that the indices are defined, where they are equal, and what quantitative results on the distance to a pair with a different index are possible. We validate a method of computing spin Chern numbers that was developed with Hastings and only conjectured to …

Principal Angles And Approximation For Quaternionic Projections [Dataset], Terry A. Loring

Math and Statistics Datasets

We extend Jordan's notion of principal angles to work for two subspaces of quaternionic space, and so have a method to analyze two orthogonal projections in the matrices over the real, complex or quaternionic field (or skew field). From this we derive an algorithm to turn almost commuting projections into commuting projections that minimizes the sum of the displacements of the two projections. We quickly prove what we need using the universal real C*-algebra generated by two projections.

Estimating Norms Of Commutators [Dataset], Terry A. Loring, Freddy Vides

Math and Statistics Datasets

We find estimates on the norm of a commutator of the form [f(x),y] in terms of the norm of [x,y], assuming that x and y are bounded linear operators on Hilbert space, with x normal and with spectrum within the domain of f. In particular we discuss |[x^2,y]| and |[x^{1/2},y]| for 0leq x leq 1. For larger values of delta = |[x,y]| we can rigorous calculate the best possible upper bound |[f(x),y]| leq eta_f(delta) for many f. In other cases we have conducted numerical experiments that strongly suggest that we have in many cases found the correct formula for the …

Computing A Logarithm Of A Unitary Matrix With General Spectrum [Dataset], Terry A. Loring

Math and Statistics Datasets

We analyze an algorithm for computing a skew-Hermitian logarithm of a unitary matrix, and also skew-Hermitian approximate logarithms for nearly unitary matrices. This algorithm is very easy to implement using standard software and it works well even for unitary matrices with no spectral conditions assumed. Certain examples, with many eigenvalues near -1, lead to very non-Hermitian output for other basic methods of calculating matrix logarithms. Altering the output of these algorithms to force an Hermitian output creates accuracy issues which are avoided by the considered algorithm. A modification is introduced to deal properly with the J-skew symmetric unitary matrices. Applications …