# Questions tagged [eigenvalues]

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### An ODE system easily polluted with spurious eigenvalues

I tried solving the eigenvalue problem of a 1st-order ODE system (see the code below) with NDEigenvalue. (One option I found in it seems to be ...
144 views

### How to control DifferenceOrder in NDEigenvalue for an ODE?

I am trying to solve the eigenvalue problem of a 1st-order ODE system using NDEigenvalue. It should be finite difference method for ODE. And I want to tune the the ...
125 views

### Why the sign of eigenfunctions obtained from NDEigensystem are flipped

I am trying to verify my hand solution for a HW problem using Mathematica. I noticed that I get correct eigenvalues from Mathematica using DEigenvalues but when ...
104 views

### Hermitian Matrix giving non-real eigenvalues

I am using the following code to find the eigenvalues of a tightbinding matrix ...
61 views

### Eigenvalues of a matrix?

I have declared this matrix in my notebook ...
469 views

### Wrong eigenvalues from a sparse matrix

Bug introduced after 5.0, in or before 8.0 and persisting through 12.0. I notice in the following example that wrong smallest 2 eigenvalues are resulted if calculating from a sparse matrix. But it ...
275 views

### Finding the eigenvalues (diagonalizing) of a block-diagonal matrix

I have a large $2^N \times 2^N$ matrix. It is the exact Hamiltonian of a spin chain model which I have generated with code I wrote in Fortran. The code block diagonalizes the Hamiltonian into constant ...
24 views

### Eigenvalues function not working properly [duplicate]

I am trying to simply find the Eigenvalues of any matrix. I have set up M to be a 3 by 3 matrix filled with random values: ...
106 views

### Problems with DEigensystem

I have the following problem $\frac{c_p q_m}{A}\frac{\partial T(x,t)}{\partial t}+\rho c_p \frac{\partial T(x,t)}{\partial x}-\lambda \frac{\partial^2 T(x,t)}{\partial x^2}=0$ I want to find the ...
78 views

### Cannot access 3-D Schrödinger eigenfunctions from NDEigensystem

The following solves the first 3 eigenvalues of the following simple 3D-Schrödinger equation, but I do not know how to use the interpolating eigenfunctions, i.e., ...
176 views

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### NDEigenvalues complains not Hermitian with large dimension differential operator

The following snippet calculates eigenvalues and eigenfunctions of a null operator (just as an example): ...
84 views

### DSolve and eigenvalues?

I have solved a system of $N$ ($N$ is the order of system) ODE with DSolve and found $N$ solutions in the form ...
35 views

### Assigning eigenkets to particular eigenspace depending on eigenvalues of system inside a module

I am writing a module, in which the Observable and State is given, so I need to write a function/module QuantumMeasurement, that will return a state of the quantum system resulting from the ...
57 views

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### Eigenfunctions to a Sturm-Liouville problem

I am trying to find the first 5 eigensolutions to a Sturm-Liouville problem; I have tried the code; ...
486 views

### How to use DEigensystem with periodic boundary conditions on the derivative?

Since I found I can use DEigensystem to obtain eigenvalues and eigefunctions for differential operators, I am using it to verify solution to some of my HW's. In ...
140 views

### Eigenvalues of a symbolic 28×28 Hessian matrix

I have a little problem trying to calculate the eigenvalues of big symbolic (depending on $a$) Hessian matrices (28×28, 32×32 ...). I think I've understand, by reading other posts, that Mathematica ...
82 views

### 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, ...
132 views

### why is there a minus sign on DEigenvalues “operator” as compared to the ODE itself?

In Mathematica, to find the eigenvalues for the following differential equation \begin{align*} y''(x)+ \lambda y(x) &=0 \\ y(0) &=0\\ y(L) &=0 \end{align*} The syntax one ...
277 views

### How to specify both DirichletCondition and NeumannValue on DEigenvalues?

Ok, I give up :) I am trying to verify the eigenvalues for heat PDE in 1D, when left end has homogeneous DirichletCondition but the right end is insulated, so it ...
363 views

### Problem with NDEigensystem

Consider the Sturm-Liouville problem $$y''(x) + \lambda x^2 y=0, \ y(0)=0,\ y(1)=0$$ The analytical solution is given by $$\lambda_n=4\alpha_n^2, \ y_n(x)=\sqrt{x}J_\frac14(\alpha_nx^2)$$ ...
314 views

### Using NDEigensystem to solve coupled eigenvalue problem

I want to find the Eigenvalues and Eigenfunctions for the following Eigenvalue problem I tried to solve this numerically ...
Consider the following coupled systems of equations $f′′− k^2 f=k\, \mathbf{Ra}$ and $g′′− k^2 g=k\,f$ , where $f$ and $g$ are functions of $z$. The boundary conditions for the problem are $f=0$ and ...