Answered
Eigenvalue doesn't zero the characteristic polynomial
The reason for this is that the characteristic polynomial for matrices of even moderate size tends to be ill-conditioned, no mat...

7 years ago | 2

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Answered
eigs does not return the eigenvalues closest to shift sigma
Hi Olivier, Yes, whether it's preferable for performance to compute more eigenvalues than needed, or to factorize the matrix ...

7 years ago | 0

7 years ago | 0

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chol() gives error for a (barely) positive definite matrix.
Short answer first: CHOL requires the input matrix to be positive definite, it does not support positive semi-definite. I'll exp...

7 years ago | 7

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eigs does not return the eigenvalues closest to shift sigma
I have not heard of this particular issue before, but I could see it happening when the eigenvalues are very clustered. If yo...

7 years ago | 0

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How to create a triangulation from a list of edges and list of nodes?
The problem is that a graph is a more general data structure than a Delaunay triangulation. Many graphs do not represent a trian...

7 years ago | 0

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optimize sequence of matlab operations for solving a system of linear equations
I assume that most of the time is spent in the line |R = K\E| (as this has cubic complexity in the size of A, while the other op...

7 years ago | 0

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relation between principal eigenvector and principal generalized eigenvector
What may be causing the differences you see is that eigs(A, B, k) first checks if the matrix B is symmetric positive definite. I...

7 years ago | 0

Answered
Is there any way to reduce the error in the calculation of eigenvectors when using eig function?
I'm just catching up on MATLAB Answers: Can you tell us some more about your problem? How are you measuring the error in the eig...

7 years ago | 0

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it is possible to get 30% of eigenvalues in short times by using the eigs(A,number, scalar) function? (A is sparse Hermitian matrix (100,000×100,000))
It's going to be expensive, but I think calling eigs(A, number, scalar) repeatedly is the most realistic way to compute 30% of t...

7 years ago | 0

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Matlab flips the eigenvalue and eigenvector of matrix when passing through singularity
The eigenvalues don't have any intrinsic order, so for real symmetric matrices, EIG just sorts them by size. Looking at just the...

7 years ago | 1

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Answered
When is eigs profitable in terms of time comparing to eig?
There is no clear answer, since this depends on many factors: - Are your matrices dense or sparse, and if they are sparse, how ...

7 years ago | 0

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Answered
Right and Left Eigenvectors
The matrices V and W contain all eigenvectors of A. For example |V(:, 1)| and |D(1, 1)| are the right eigenvector and eigenva...

7 years ago | 0

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How can I find circle diameter using arc ?
There's a recent blog post by Loren on fitting a sine wave to a picture by eye: <https://blogs.mathworks.com/loren/2018/06/04...

7 years ago | 0

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Calculating gradient for equation in higher dimension?
If the matrices and ND-arrays are of a fixed dimension, you can create symbolic variables for them: A = sym('A', [3 3 3]) ...

7 years ago | 1

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Matlab internal parallelization not working (?) under linux
You can also use maxNumCompThreads to set the maximum number of computational threads you want MATLAB to use. So for example, yo...

7 years ago | 0

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Hellow, I have a problem To obtain participation factors, and specifically with the right and left eigenvectors in a paper I was reading about it, related in Power sistems, so Im tryin to use eig but the result are not the same: thank you 4uhelp
Hi, The eigenvalues and right-side eigenvectors are correct, they are just returned in a different order than you assume: ...

7 years ago | 2

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Answered
Using sparse/full to solve Ax = b
If A is sparse and b is dense, x = A\b returns a dense matrix x, so no need for the "full" command. It's also not necessary to m...

7 years ago | 1

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Decomposition object saveobj method not supported?
This is a limitation on the decomposition object: It cannot be saved into .mat file. The background for this is that some types ...

7 years ago | 1

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Answered
Matlab internal parallelization not working (?) under linux
You can use the function |maxNumCompThreads| to see the maximum amount of threads MATLAB uses.

7 years ago | 0

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bugs in eig?
Both answers are correct. The eigenvectors of a matrix are not uniquely determined: Every eigenvector can be multiplied by an ar...

8 years ago | 1

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How to identify repeated eigenvalues of a matrix?
For general matrices, the eigenvalues will typically have a bit of round-off error, so repeated eigenvalues will not be exactly ...

8 years ago | 0

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How to add edges to a graph plot using GraphPlot handle?
There is currently no way to do this, the edges and nodes must be modified on the |graph| or |digraph|, and then this can be pas...

8 years ago | 0

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Answered
Eigs yields different results on different versions
Numerical results can change between versions, and for eigenvectors, it's possible that several eigenvectors have the same or ve...

8 years ago | 0

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How to improve speed of calculating trace in a script?
You can make the trace operator work faster as follows: Currently, the input is two truncated SVDs, |A1 = U1 * S1 * V1'| and |A2...

8 years ago | 1

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Answered
How to find the permutation matrix for the qr decomposition?
You need to compute all three matrices together: Q and R are different if the third output e is also returned. For an algorit...

8 years ago | 2

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How to find the permutation matrix for the qr decomposition?
I'm afraid using the three-output syntax is the only way. You can use [~, ~, p] = qr(A); but Q and R are still computed,...

8 years ago | 0

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Nonconvex: Checking positive-semidefiniteness inside the Gloptipoly package
For positive definiteness, I would recommended to check this using CHOL (see if the second output registers a problem), but this...

8 years ago | 0

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Answered
Order of eigenvalues depending on matrix equation order of operations
The reason for the difference in this case is that matrix B is exactly symmetric, and matrix A is not. EIG detects if the input ...

8 years ago | 1

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Answered
Examining entries in binary matrices and creating new group matrix based on % of connections (defined by 1)
If you have each matrix stored in a separate variable, you can do Atotal = A1 + A2 + A3; % Sum of logical matrices is...

8 years ago | 0