# Tag Info

### How to check if a vector is an eigenvector of a matrix using mathematica?

You could use MatrixRank. Here is a function that does this: ...
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### Complex eigenvalues from a sparse Hermitian matrix

Very good observation. Indeed, this issue is really frustrating. To single out the issue: It seems that Arnoldi's method is to blame: ...

### Eigenvalues broken in Version 12.0

Not a solution but too big for a comment. There seems to be a catastrophic failure in Eigenvalues happening that is not due to the matrix being crazy. As a ...
• 48.4k
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### Eigenvalues broken in 11.2?

This is a bug. The problem seems to be related to the fact that some rows of your matrix are packed arrays and some are not. ...
• 236k
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### Making an interactive visualization of the eigenvectors of two-dimensional matrices

The following is an attempt to recreate a similar sort of interactive visualization, showing the eigenvectors (when real), and how the various points of the unit circle are transformed by the matrix. ...
• 7,663
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### Finding Eigenvalues for a boundary value problem

Update: This implementation is now a package called CompoundMatrixMethod, hosted on github. It can be installed easily by evaluating: ...
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### Library for FEAST method is missing

I just wanted to a bit more context here, and it is too long for a comment. First, there have always been platform differences in the available features, going back to V1. These were mostly on the FE ...
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### Library for FEAST method is missing

I contacted the customer support and got the following reply: "The 'FEAST' method for functions like Eigensystem is part of the Intel MKL library, and as such will not be available to non-Intel ...
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### Eigendecomposition of a matrix with a variable

Your eigenvectors in EigenVec are normalized but not orthogonal to each other, as you can see using ...
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### Solving the Schrödinger Equation by exact diagonalization

Eigenvalues and Eigenvectors return the eigenvalues sorted from highest to lowest. From the documentation: Eigenvectors with ...
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### How to numerically solve the Schrödinger equation for Lennard-Jones potential?

Here is a modified version of my answer to How to numerically solve a 1-d time-independent SchrÃ¶dinger equation? that solves this problem. I use NDEigensystem ...
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### Eigenvalues broken in Version 12.0

Edit: Eigensystem fixed in 12.1 in addition to Eigenvalues I attempted a workaround, to see if Eigensystem had any issues also. It does. This is very unfortunate. ...
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### Lowest Magnitude Eigenvalues of Large Sparse Matrices

Use the Arnoldi method with shift-inversion: Eigenvalues[A, 3, Method -> {"Arnoldi", "Criteria" -> "Magnitude", "Shift" -> 0}] gives you the three ...
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### Routh-Hurwitz criterion not giving correct answer when done manually?

I can't say why your approach didn't work, but my RouthHurwitzCriteria function uses a simplified test for 3x3 matrices due to Fuller (1968), which I first learned about from Gandolfo (1997): There ...
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### Is there a bug in Eigensystem[]?

Notice that there are two eigenvalues, both degenerate: ...
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### Solving this challenging ODE

I have a package for solving eigenvalue boundary value problems using the Compound Matrix Method with the Evans function, which is ideally suited to this. The package is available on my GitHub, a ...
• 5,663
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### Wrong eigenvalues from a sparse matrix

It appears that the proximity of the eigenvalues causes Eigensystem with the default parameters to be inaccurate. This can be fixed by increasing the basis size to 30 ...
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### How to set interface conditions for optical waveguide in NDEigensystem?

There are three conditions when we want to get eigenfunctions in Cartesian coordinates, similar to eigenfunctions in cylindrical coordinates. The first is the correspondence of boundaries. The second ...
• 45.8k
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### Eigenvalue problem

Weak method, the solution converges to the exact one at Nn >= 200. It takes time. Figure 1 shows the solution for Nn=100, 200 ...
• 45.8k
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### Fast method to calculating signature of a matrix

SeedRandom[1]; H = RandomReal[{-1, 1}, {100, 100}] // (# + #\[ConjugateTranspose]) &; Short[H, 3] ...
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### How to normalize a list of eigenvectors?

Here's a range of incremental improvements: ...
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### Tracking Eigenvalues Through a Crossing

I'm not sure this will be robust enough for a 48 x 48 matrix. The idea is common enough: Build an interpolation of a function by integrating its derivative with ...
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### Noise in Eigenvalues plot

By default, the eigenvalues are ordered by absolute value. All the eigenvalues of this particular matrix have the same absolute value plus some rounding errors. Thus, it can easily happen, that the ...
Accepted

### Eigenvalues broken in Version 12.0

Fixed in 12.1 ...
• 146k