# Tagged Questions

Questions on the manipulation of matrices in Mathematica.

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### How to compare and remove x-coordinates (and the associated y-coordinates) that are less than previous x-coordinates?

I am using Mathematica version 9.0 and am trying to compare and remove x-coordinates, and the associated y-coordinate, that are less than previous x-coordinates. Below is an example using sample data. ...
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### Simplest use of transpose given a vector and a matrix [closed]

Suppose that I have: x = {1, 1}/Norm[{1, 1}]; A = {{1, 2}, {2, 1}}; What is the simplest way of calculating $x^T A\ x$? And are there symbols on any of the ...
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### Is Eigensystem::eivin message a bug?

I noticed that in the question Request for clarification of Eigensystem::eivn message the error message Eigensystem::eivn: Incorrect number 2 of eigenvectors for eigenvalue Root[<<14>>+(<&...
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### Multiplying three matrices does not give expected form [closed]

I'm having lectures on analytic geometry. I've learned that there is an associated matrix multiplication for a quadratic form: \$\quad \quad \left( \begin{array}{ccc} x & y & 1 \\ \end{array} ...
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### Eigenvalues function not producing expected results?

I'm running into a strange issue when trying to compute eigenvalues of a 2x2 matrix for graphene. If I "manually diagonalise" by multiplying the two off-diagonal terms together and taking the square ...
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### How to get simultaneous eigenvectors of commuting matrices? [duplicate]

So let's say there are two square matrices A and B that commute (AB-BA=0). This implies that there must exist some complete set of vectors that are eigenvectors of both A and B. Is there any way to ...
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### How to get Complement function working in a For loop? [closed]

I've been working on a piece of code that will delete small components from a nested uneven matrix (n pages, n rows, 3 columns), by deleting the pages with less than ~30 rows. However, I've notice ...
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### Can I rely on the ordering of the adjacency matrix? [closed]

Suppose I have created a Graph[{1,2..n}, {1->3, etc}], and I take the adjacency matrix of that graph. Can I rely on the fact that the i-th entry in the graph is the i-th node in the matrix? Or maybe ...
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### Does a matrix need to be rationalized when calculating MatrixExp? [closed]

I have a sparse matrix, L, and need to calculate its exponential, MatrixExp[L t], where t is ...
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### Having trouble translating Matlab fsolve` into Mathematica

I searched the site and found that someone said FindRoot is equivalent to fsolve, however, without proper options, ...
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### Matrix with known entries but unknown size [closed]

I am trying to perform some calculations with a matrix that has let's say size N but unknown, please How can I write this in mathematica?