# Questions tagged [eigenvalues]

Questions on symbolically or numerically determining the eigenvalues of matrices (Eigenvalues, Eigensystem) or differential equations (DEigenvalues, DEigensystem, NDEigenvalues, NDEigensystem) in Mathematica. Also includes determining the eigenvalues of differential equations with DSolve or NDSolve.

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### What algorithm is Mathematica using to find the smallest eigenvalue so quickly?

My question is what kind of black magic is Mathematica doing to obtain the correct answer so quickly compared to other programming languages? Details: I've written a Mathematica notebook to find the ...
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### Numeric Solution Hydrogen Atom

I'm trying to solve the Schrödinger equation for the hydrogen atom without made the variable separation of the polar and radial coordinate. It is my test code to extrapolate to another system with its ...
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### DEigenvalues and NDEigenvalues return different values

In the following example, DEigenvalues and NDEigenvalues return different results despite having identical arguments. Does anyone know why? (I use Mathematica 11.3) ...
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### How to compute eigenvalues of linear function (not matrix)?

How to compute eigenvalues of a known linear function? In Julia, there is a package https://jutho.github.io/LinearMaps.jl/dev/ to compute the matrix representation of given function, then we can ...
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### Differing behavior of Eigenvalues and Eigensystem

With the update to v12.0, I seem to be getting different behavior of eigenvalues returned by Eigenvalues and Eigensystem (oddly, ...
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### Memory usage for smallest eigenvalues

I have a bunch of hermitian matrices which are huge (of order 2^17 x 2^17) but extremely sparse so that, when I build the matrices, the usage of RAM is low (say of order 1 GB or similar). The ...
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### Solving a matrix pencil (quadratic eigenvalue) problem with Mathematica

According to Wikipedia The matrix pencil of degree $\ell$ is the matrix-valued function defined on the complex numbers $L(k) = \sum_{i=0}^{\ell} k^{i} A_{i}$. Here $A_{\ell}$ are non-zero $n\times n$...
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### Does current Mathematica capability allow solving PDEs (e.g. reaction diffusion equation) over surface of a mesh or surfaces

I came across this nice paper (https://arxiv.org/pdf/1605.01583.pdf) where the authors simulated a reaction diffusion system over the surface of a gecko, primarily to understand how various patterns ...
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### Finding matrix in Krylov subspace (Lanczos method)

The Lanczos method for finding the smallest eigenvalue of a hermiteian matrix $H$ is based on the construction of a vector subspace (Krylov space) where one can build a matrix $H_{Krylov}$ which is ...
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### Difference in computation speed of Eigensystem not to expectation for ParallelTable and Table

I was trying to compute the time it takes for Eigensystem to evaluate while being inside a ParallelTable, as it is well-known LAPACK subroutine has an inbuilt Parallelization to it. And the difference ...
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### Orthogonal matrix decomposition of symmetric matrix?

If matrix mat is symmetric, we should be able to decompose it into eigenvalue matrix matJ and orthogonal matrix ...
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### What real symmetric matrices of this type can Mathematica find symbolic eigenvalues for?

I'm working on a problem calculating symbolic eigenvalues of matrices that always have a very simple form: they are real and symmetric and usually sparse. They have two distinct symbolic parameters. (...
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### First few smallest eigenvalues of a large dense symmetric matrix

I construct a large (say 2000x2000) matrix M whose entries are real random variables drawn from a certain distribution. Most of these values will be nonzero, so <...
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### (Possibly bugs? ) Wrong results provided by DEigensystem

I was trying DEigensystem with the following code: ...
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I refurbished my post in order to be more understandable. After computing simulations of Chladni patterns with Mathematica (see my previous topics), I finally went to practice. I realized my own ...
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### Derivative of eigenvalues

I work with 4x4 Hermitian matrices (r). I want to calculate a derivative of a function f[t,r] (ff[t_,r_]=1/2*D[f[t,r],t]), where the function f depends on the absolute value of the eigenvalues of r. ...
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### Interface points of NDEigensystem

When solving an eigenvalue problem with "NDEigensystem", e.g. a 1D Eigenvalue problem with the interval composed of different materials, which should be solved by the pure numerical method such as FEM,...
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### How to get single $n^{th}$ eigenvalue and eigenfunction using NDEigensystem?

I am trying to solve the Schrödinger equation for a $2D$ Harmonic Oscillator using the following codes. Code-1 ...
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### What kind of performance should I expect out of Eigensystem using FEAST?

I'm numerically solving a time-independent Schrödinger equation using Eigensystem's FEAST method. It takes a lot longer than I ...
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### Block diagonalizing a complex anti-symmetric matrix

I am going to evaluate the block diagonal form of few skew-matrices. When matrix elements are real I can simply follow the approach suggested in this thread which I have implemented that as ...
• 1,043
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### Boundary value problem, multiple dimensional shooting, coupled eigenvalue problem

Following the one dimensional boundary value problem here, I would like to understand the easiest way to solve a BVP for a coupled system. In the 1D case, BVP can be converted to an initial value ...
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### DEigenvalues with Robin B.C. sign problem

To find eigenvalues for $y''=\lambda y$ with robin boundary conditions on one end, and Dirichlet on the other end, I am getting correct value when robin B.C. on the right side, but when I flip things, ...
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### Eigenvector matrix of a real positive matrix to be from $SO(n)$. How?

Suppose I have a positive real matrix of dimension $n$ and as such there exists a diagonalizing (rotation) matrix that belongs to $SO(n)$. How do I force Eigensystem...
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### Numerical ground state wavefunction of Schrödinger equation with a Coulomb potential in 2D from NDEigensystem

I want to numerically solve the ground state wave function of the hydrogen atom with the Coulomb potential using the NDEigensystem. Here is the code to get the ground state wave function from the ...
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