# 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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### How can I get rid of Abs?

In the following code, the functions WP[t] and WS[t] are real. Time also is a positive parameter. As you can see, MATHEMATICA enters Abs in the calculations. Including Abs only complicates the next ...
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### how can I correct this code? [duplicate]

I need to calculate matrix m1 according to following algorithm. Then, I have to put it in the differential equation. However, matrix m1 is complex and therefore the differential equation does not work....
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### How can I correct this code to get an answer? [duplicate]

I need to calculate matrix m1 according to following algorithm. Then, I have to put it in the differential equation. However, matrix m1 is complex and therefore the differential equation does not work....
116 views

### Solving Helmholtz equation in 3D for torus

How I can solve the Helmholtz equation in 3D domain? According to the following post, I encounter an error when I run the program. Any help would be graet! Numerically solving Helmholtz equation in 3D ...
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### How to solve the following equation numerically?

In the following code, if the matrix "n = (-I*(m1)) + (m2)" in the differential equation contains only the matrix "m1", I will get the answer, but if the matrix "n" is ...
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### Effectivelly using Compile for calculate a Unitary transformation

I am new to Mathematica, and this is my first post, so if my question is not clear enough, I would be glad to read the comments and edit my question to add more information. The problem I need to ...
154 views

### Plotting Eigenvalues and severe Noise Problems

I am trying to plot Eigen values of my System Hamiltonian in Mathematica. This is generating very noisy plot. This is my code. ...
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### Integrate over one variable of a 2D interpolating function returned from NDEigensystem

I'm trying to implement the answer for "Integrate only one variable of a 2D interpolating function" (https://mathematica.stackexchange.com/a/161962/73672) but for interpolating functions ...
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### Removing Unwanted Eigenvalues, Twisted bilayer Graphene Hofstadter Butterfly

I am plotting eigen values of a matrix. I want to remove unwanted eigenvalues from the plot. For try run this is possible to manually remove these unwanted eigen values. But for actual run this is not ...
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### Mathematica precision on extensive eigenvalues calculations

Im trying to evaluate some dot products with eigenvectors and matrices using Mathematica. My problem is the following: To an given matrix 6x6: ...
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### Eigenvectors for two very close matrices [closed]

I have two matrices. ...
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### Numerical eigenvalues of the problem

I have this equations with condition 0 <= x <= 1: ...
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### Find the eigenvalues of 3-coupled equations matrix

I'm trying to solve and and get the Eigenvalues (Natural frequencies later) of the matrix 3x3 for 3 Galerkin equation like in the pictures,,, where I solved them with one mode easily but with these ...
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### How to collect the negative eigenvalues of a matrix?

I want to plot Sum[E[i]] verseus t where E[i] are the negative eigenvalues of the matrix: <...
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### Finding eigenvalues of a large ( >1000 x 1000) matrix accurately

I'm doing a spectral method-based eigenvalue problem where I create a matrix, A, of size (nr+1)(nz+1)(2nf+1) where nr,nz,nf are integers, composed of a diagonal of (2nf+1) submatrices of size (nr+1)*(...
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### Strange numerical values of Eigenvectors

When I calculate Eigenvalues and Eigenvector by using: Eigensystem[{{3.8, 21, 21}, {0.3, 3.5, 2.5}, {-0.8, -6.2, -5.2}}] I get the following result: ...
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### What does Eigensystem::geinsl1 mean (a solution for the generalized eigenproblem may be incorrect)?

I'm trying to solve a generalized eigenvalue problem and ran across a warning Eigensystem::geinsl1: Warning: a solution for the generalized eigenproblem may be incorrect. Here's a minimal working ...
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### How can I improve the speed of computing of numerical integration and eigenvalue?

First, let me explain what I am calculating. I have the following 2D-equation: $$w(x,y) = \sum_{m}^{M}\sum_{n}^{N}A_{mn}\sin\left(\frac{2m\pi x}{a}\right)\sin\left(\frac{2n\pi y}{b}\right)$$ ...
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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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### Undesired complex number in the square root

I am trying to solve the eigenvalues of a hamiltonian The code I used is typed below. ...
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### Help in modifying my code

In my code, I want to plot (Dis[t]). The problem is some functions containing in the code do not work well if there are variables in the form of symbols, such as "Sort" "NMaximize" functions. I want ...
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### Mathematica outputs its input; Eigensystem [duplicate]

I am simply trying to find the eigenvalues of a symbolic matrix using Matematica, but it does not give me an answer; it just outputs its input. (u is a parameter) ...
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### Find minimal recoding of the (symbolic) entries of an $8 \times 8$ matrix

I have the following $8 \times 8$ matrix ...
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### Arnoldi method misses eigenvalues degeneracies for very sparse matrices

I am here to signal a problem very very similar to the one already discussed here Wrong eigenvalues from a sparse matrix In particular, I have a very sparse matrix and I am asking just few dominant ...
How can I numerically compute the first (non-negative) eigenfunction $u$ of the $p$-Laplacian ($p>1$) in a bounded interval $(-a,a) \subset \mathbb R$ (up to positive multiplicative constant)? -\...