Burda Zdzislaw, Livan Giacomo, Swiech Artur
Marian Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland and Mark Kac Complex Systems Research Centre, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland.
Phys Rev E Stat Nonlin Soft Matter Phys. 2013 Aug;88(2):022107. doi: 10.1103/PhysRevE.88.022107. Epub 2013 Aug 7.
Ensembles of isotropic random matrices are defined by the invariance of the probability measure under the left (and right) multiplication by an arbitrary unitary matrix. We show that the multiplication of large isotropic random matrices is spectrally commutative and self-averaging in the limit of infinite matrix size N→∞. The notion of spectral commutativity means that the eigenvalue density of a product ABC... of such matrices is independent of the order of matrix multiplication, for example, the matrix ABCD has the same eigenvalue density as ADCB. In turn, the notion of self-averaging means that the product of n independent but identically distributed random matrices, which we symbolically denote by AAA..., has the same eigenvalue density as the corresponding power A(n) of a single matrix drawn from the underlying matrix ensemble. For example, the eigenvalue density of ABCCABC is the same as that of A(2)B(2)C(3). We also discuss the singular behavior of the eigenvalue and singular value densities of isotropic matrices and their products for small eigenvalues λ→0. We show that the singularities at the origin of the eigenvalue density and of the singular value density are in one-to-one correspondence in the limit N→∞: The eigenvalue density of an isotropic random matrix has a power-law singularity at the origin ~|λ|(-s) with a power sε(0,2) when and only when the density of its singular values has a power-law singularity ~λ(-σ) with a power σ=s/(4-s). These results are obtained analytically in the limit N→∞. We supplement these results with numerical simulations for large but finite N and discuss finite-size effects for the most common ensembles of isotropic random matrices.
各向同性随机矩阵系综由概率测度在任意酉矩阵的左(及右)乘下的不变性来定义。我们证明,在无限矩阵规模(N→∞)的极限情况下,大的各向同性随机矩阵的乘法在谱上是可交换的且是自平均的。谱可交换性的概念意味着这种矩阵的乘积(ABC\cdots)的特征值密度与矩阵乘法的顺序无关,例如,矩阵(ABCD)与(ADCB)具有相同的特征值密度。反过来,自平均的概念意味着(n)个独立但同分布的随机矩阵的乘积,我们用(AAA\cdots)来象征性地表示,其特征值密度与从基础矩阵系综中抽取的单个矩阵的相应幂次(A^{(n)})相同。例如,(ABCCABC)的特征值密度与(A^{(2)}B^{(2)}C^{(3)})的特征值密度相同。我们还讨论了各向同性矩阵及其乘积对于小特征值(λ→0)时特征值和奇异值密度的奇异行为。我们表明,在(N→∞)的极限情况下,特征值密度和奇异值密度在原点处的奇点是一一对应的:当且仅当各向同性随机矩阵的奇异值密度具有幂律奇点(\simλ^{(-σ)})且幂次(σ = s/(4 - s))时,其特征值密度在原点处具有幂律奇点(\sim|\lambda|^{(-s)})且幂次(s∈(0,2))。这些结果是在(N→∞)的极限情况下通过解析方法得到的。我们用大但有限的(N)的数值模拟来补充这些结果,并讨论最常见的各向同性随机矩阵系综的有限尺寸效应。