Christine Tobler

MathWorks

Last seen: Today | Active since 2015

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Spoken Languages:
English, French, German
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Professional Interests:
Graph and Network Algorithms, Linear Algebra, Quantum Computing

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Answered
NaN output only when using three ouput for QR
The 3-output syntax and the 2-output syntax of QR use different implementations, so that's likely the reason you're seeing diffe...

24 dagen ago | 1

Answered
In a (possibly directed) graph, is there a simple way to find all nodes reachable for a given node?
The quickest way to find all nodes reachable from a given node is using the nearest function with Inf as the distance: g = digr...

ongeveer een maand ago | 1

Answered
eig() working where eigs() doesn't
The 'largestreal' option can be useful, but this depends on the problem. The iteration inside eigs will naturally find the eigen...

2 maanden ago | 0

Answered
Should mldivide Return a Solution for Square, Rank-Deficient, but Consistent Set of Linear Equations?
Hi Paul! You can use x = linsolve(A, b, struct('RECT', true)); to use the QR method of mldivide even if A is square. To get ...

2 maanden ago | 3

| accepted

Answered
how can improve limitation of input simulation function of quantum circuit.limitation is number of qubits
The limit of 20-30 qubits is what would be expected for a state vector simulation, which requires a vector of length 2^NumQubits...

4 maanden ago | 0

Answered
Problem in assigning proper eigevalues in a for-loop
Sorting the returned eigenvalues by their real part (since you are plotting only the real part of the eigenvalues) should help. ...

4 maanden ago | 0

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Answered
polyeig calculating few polynomial eigenvalue
While there is no equivalent to eigs for polyeig, if you just need some eigenvalues, you could step through polyeig.m and get wh...

4 maanden ago | 0

Answered
Numerical search for the singular points of a complex matrix
From your description, it appears you have a nonlinear eigenvalue problem (a matrix A(lambda) where you are looking for a comple...

4 maanden ago | 0

Answered
Non Linear Eigenvalue problem
Sorry for answering so long after the initial post. One option you could consider for solving a nonlinear eigenvalue problem is ...

4 maanden ago | 0

Answered
Incorrect evaluation by Composite Quantum Gate
The issue is a typo in your code. Instead of constructing 3 identity gates, your third gate is an X gate: innerUGates = [idGate...

7 maanden ago | 0

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Answered
Remove node and reconnect edges in a very large graph
It is usually best to first compute all the edges / nodes to act on, and then modify the graph in one step with all of them: G1...

8 maanden ago | 0

Answered
How to find the best solution to make eigs function converge?
It seems that the eigenvalues of H are pure imaginary (I'm seeing real parts of magnitude about 1e-14, and the maximum imaginary...

9 maanden ago | 0

Answered
Call to inv() function seems to have (undesired) impact on Thread pool or maxNumCompThreads()
I asked around internally, and there was an issue that looks very similar in R2023b that has been fixed in R2024a. If you have R...

9 maanden ago | 0

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Answered
solving linear system with decomposition(A,'qr') and qr(A) produce different results
There are two reasons that the results don't match: 1) When the matrix is not full-rank, the QR-based solver in decomposition o...

10 maanden ago | 1

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Answered
What is the most computationally efficient factorization of a matrix A?
Your solution is correct. Of the factorizations you know (PA=LU, the Choleski, SVD and the QR factorization), only LU and Chole...

11 maanden ago | 1

Answered
Improving Precision of Eigenvectors with Large Eigenvalues
The linked post is about a symmetric matrix, is this also your case? In that case (if issymmetric returns true for your matrix),...

11 maanden ago | 2

| accepted

Answered
Join Subgraphs into a new Graph
Here's a quick example based on a guess at how you would like to merge the graphs: G1 = graph(["A" "B" "C"], ["B" "C" "D"]); G...

11 maanden ago | 1

| accepted

Answered
how to increase node/edge separation within the layer in the layered graph?
You can access the XData and YData properties of the GraphPlot object returned by plot, to move the nodes further apart. Note i...

11 maanden ago | 0

Answered
Nonorthogonal eigenvectors for general eigenvalue problem with eig() and eigs()
For simple eigenvalue problem A*x = lambda*x, the eigenvalues are real and the eigenvectors can form an orthogonal basis only if...

12 maanden ago | 0

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Answered
Name for adjancy-to-graph algorithm?
The graph object in MATLAB uses an internal data format that is very similar to a sparse adjacency matrix, so the construction o...

12 maanden ago | 0

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Answered
Convert an image to a graph object
From a graph theory perspective (others may have better ideas from the image processing side), I would start by making a graph o...

ongeveer een jaar ago | 0

Answered
eigs with complex hermitian matrix, should I set opts.issym to 1?
This only matters if you pass in a function handle - if you pass in a matrix, EIGS detects if it's hermitian (real or complex) d...

ongeveer een jaar ago | 0

Answered
Cyclebasis function for graphs not working
Yes, cyclebasis returns a fundamental cycle basis, but not necessarily the one with the shortest cycle lengths. See the document...

ongeveer een jaar ago | 1

| accepted

Answered
SVD computation time question
I'm not sure what causes the sharp change between iterations - I can reproduce roughly similar timings when I call svd with 3 ou...

ongeveer een jaar ago | 1

| accepted

Answered
What is the residual defined in eigs?
The issue is likely that eigs doesn't use the residual as you describe it: The iterative algorithm used inside of eigs when comp...

ongeveer een jaar ago | 0

Answered
LU decomposition with 5 output arguments
As Matt says, the simplest is likely to just use decomposition object. In terms of how to solve a linear system, the doc page g...

ongeveer een jaar ago | 2

| accepted

Answered
Proper Installation of Tensor Toolbox
Find the path the folder that defines the class you want to use. My guess is for Tucker this will be the ttensor class (but it's...

ongeveer een jaar ago | 0

Answered
Computing eigenvalues and eigenvectors of two symbolic matrices
eig does not support the two-input syntax for symbolic. For the call eig(B, A), if A is invertible you can instead solve eig(A\B...

ongeveer een jaar ago | 0

Answered
Stability analysis of a time dependent Lyapunov equation
The tensorprod function doesn't do what you are looking for here, that would be kron (short for Kronecker product). It also see...

ongeveer een jaar ago | 0

Answered
getting warning while using eigs on the matrices obtained from freefem++
If modifying the input sigma doesn't help, it's likely that for your call eigs(A, B, sigma, ...) the matrices are such that A - ...

meer dan een jaar ago | 0

| accepted