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# Christine Tobler

### MathWorks

221 total contributions since 2015

Professional Interests: numerical linear algebra, graph algorithms

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Eigenvectors and the null function
I'm getting those two eigenvectors when I copy your code into MATLAB: >> D = [2 -1; -1 3]; eigs = eig(D); q1 = nu...

1 day ago | 0

Block-diagonalization of a matrix
There is no direct function to do this. The best is probably to write a function that does a loop through the different blocks a...

1 day ago | 0

How created a graph from unordered node list?
When a graph or digraph is specified using numbers, the assumption is that all nodes of this graph have numbers from 1:numberOfN...

2 days ago | 0

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nonsingular matrix (X) in GSVD function
These are just different but equivalent definitions: Both will result in the same C and S, the only difference is in how X is re...

2 days ago | 0

accuracy of two methods to solve eignvalues/eignvector problem
The second way is typically more accurate, because it doesn't incur additional round-off error when conputing inv(Sw) and when m...

5 days ago | 0

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Sort eigenvectors matrix.
Take a look at rsf2csf. For a block-diagonal matrix with 1-by-1 and 2-by-2 blocks, it computes a diagonal eigenvalue matrix and ...

13 days ago | 1

Eigenvectors of an SPD matrix being saved as complex doubles
EIG does not recognize the input matrix as symmetric because it's not exactly symmetric. If you compute A = Y'*Mh*Y norm(A - A...

16 days ago | 0

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Given a matrix A^n. Comparing normal multiplication versus Diagonalization. I expect the former to be faster but its not in my case
A^2 is just one matrix multiplication, A*A, which is much faster to do directly than the call to EIG. For larger n, A^n isn't ...

1 month ago | 0

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how to random initialize svd function in matlab??
The linear algebra functions in MATLAB are run-to-run reproducible, meaning if you call them twice with the exact same input, yo...

1 month ago | 1

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EigenValues of a Vibrating system
Usually for finite element problems, the stiffness matrix is passed in as the first input, and the mass matrix as the second inp...

1 month ago | 0

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issues with Cholesky decomposition
This can happen if your matrix is close to symmetric positive semi-definite (meaning the smallest eigenvalue is around machine e...

1 month ago | 0

Can I preserve adding order when calling graph/addedge?
The edges in a graph are always presented in the same order (sort first by source node, secondarily be target node). You can mai...

1 month ago | 1

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Display only one eigenvalue of symbolic matrix
The eigs function is not supported for symbolic values, as it is specifically based on getting a good approximation based on an ...

2 months ago | 0

how to do forward neighbor discovery in un-directed graph?
If I understand correctly, you want to find all nodes that are direct neighbors of n1, then all nodes that connect to n1 through...

2 months ago | 0

Using eigs with singular matrix
The 'smallestabs' option in eigs depends on solving several linear systems with the matrix A that's being passed in. If A is sin...

2 months ago | 0

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Change the alignment and font size of edgelabels
The edge labels provided with the plot of a graph can't be modified in terms of their alignment. However, you can add standard t...

2 months ago | 0

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a question for defining Custom Deep Learning Layer
You can use the svd in a custom layer, however, if the SVD is used in the forward method of a custom layer, this will likely req...

2 months ago | 0

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Control edge alpha via edge weights to visualize a dynamic network
You can set the LineStyle to be 'none' for edges that should not be displayed: >> g = digraph([3 1 2], [2 3 1], [0 0.5 1]); >>...

2 months ago | 1

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how to create a symmetric Toeplitz matrix with bounds on eigenvalues?
You can use the MATLAB function toeplitz with one input argument (two-input returns a non-symmetric Toeplitz matrix).

2 months ago | 0

Interpolation for n-dimensional array data
I don't think interpn would work very well for you: The U, S and V matrices returned by SVD are not linearly dependent on the in...

3 months ago | 1

eigs gives wrong eigenvalues
Edit: Please see the comment below, the first answer I gave here was going in the wrong direction. Thank you for the detailed d...

3 months ago | 2

How can I solve linear equation system in parallel?
As John says, if you are using decomposition on one computer with several cores, the solver used already will use those cores if...

3 months ago | 1

Why Power of Matrix with decimal values gives really big numbers?
For a Markov Chain, you need the sum of each row to be 1 (as this represents the probability to transition to any state), and ev...

3 months ago | 0

Which Right Eigenvector to report?
The left and right eigenvectors are matched one-by-one. For example, for [V, D, W] = eig(A), the eigenvalue D(k, k) corresponds ...

3 months ago | 0

eigs for generalized eigenvalue problem ( [V,D] = eigs(A,B) ) with spars matrix
A bug was introduced in R2017b in eigs for matrices with exact zero eigenvalues. This bug has been fixed in R2019a, the fix appl...

4 months ago | 1

Error using eig Input matrix contains NaN or Inf from images
The variable covariance_matrix contains non-finite values (either Inf meaning infinity, returned for example from 1/0, or NaN me...

4 months ago | 0

Why are eigenvector matrices computed by matlab not idempotent
Hi Marco, You seem to be confusing two terms: A matrix M is idempotent if ; it's orthogonal if , which is what you are testing ...

4 months ago | 2

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Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 7.252760e-17.
As lambda approaches an eigenvalue of A (which is the goal of your algorithm), the matrix A - lambda*eye(size(A)) becomes close ...

4 months ago | 1

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How to compute efficiently A^(-1)*(1-exp(-A*h))?
For most sparse matrices expm(A) will be dense, so that should be expected to be expensive with a 1e4-by-1e4 matrix. If you are ...

4 months ago | 0

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