Christine Tobler
MathWorks
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Graph and Network Algorithms, Linear Algebra, Quantum Computing
English, French, German
Pronouns:
She/her
Professional Interests:
Graph and Network Algorithms, Linear Algebra, Quantum Computing
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Answered
How does the svd function determine or fix the phase of singular vectors?
Hi Lv-lin, 1. MATLAB computes SVD internally through a completely separate algorithm than EIG, with both algorithms provided b...
How does the svd function determine or fix the phase of singular vectors?
Hi Lv-lin, 1. MATLAB computes SVD internally through a completely separate algorithm than EIG, with both algorithms provided b...
6 days ago | 1
Answered
Iterating the eigenvalue function (eig) produces patterns --- is this a well known result?
Hi David, This is very interesting! To answer your questions: oo one question is, is this well known behavior? I'm not awa...
Iterating the eigenvalue function (eig) produces patterns --- is this a well known result?
Hi David, This is very interesting! To answer your questions: oo one question is, is this well known behavior? I'm not awa...
15 days ago | 0
Answered
double free or corruption (out) error when using MATLAB Runtime 2023b
This seems to point to a memory corruption, the source of which is always hard to pinpoint (since the corruption could have happ...
double free or corruption (out) error when using MATLAB Runtime 2023b
This seems to point to a memory corruption, the source of which is always hard to pinpoint (since the corruption could have happ...
2 months ago | 0
Answered
Calculate eigenfunctions to known eigenvalues
Unfortunately, there isn't a painless way to do this. That is, it's likely that writing new code to get eigenvectors given the e...
Calculate eigenfunctions to known eigenvalues
Unfortunately, there isn't a painless way to do this. That is, it's likely that writing new code to get eigenvectors given the e...
2 months ago | 0
| accepted
Answered
Backslash (mldivide) slower than inverse and multiplication
Hi AB, This is an interesting question. The conventional wisdom is based on the computational complexity, meaning it prioritize...
Backslash (mldivide) slower than inverse and multiplication
Hi AB, This is an interesting question. The conventional wisdom is based on the computational complexity, meaning it prioritize...
3 months ago | 10
| accepted
Answered
Symbolic Eigenvalue Assignment with Matlab Symbolic Math Toolbox
It seems that the svd function in Symbolic Toolbox supports the one-output syntax in general, but only supports the 3-input synt...
Symbolic Eigenvalue Assignment with Matlab Symbolic Math Toolbox
It seems that the svd function in Symbolic Toolbox supports the one-output syntax in general, but only supports the 3-input synt...
4 months ago | 0
| accepted
Answered
real power of matrices
I'm not seeing the described behavior: x = [1 0 0; 0 1 0; 2 3 1]; y = mpower(x, 0.5) y*y Can you try to rerun the code?
real power of matrices
I'm not seeing the described behavior: x = [1 0 0; 0 1 0; 2 3 1]; y = mpower(x, 0.5) y*y Can you try to rerun the code?
4 months ago | 0
Answered
How does Matlabs svd() function calculate the value of V?
Hi Caleb, Happy to discuss the svd with you! That being said, as others here have mentioned, svd is a building block and not e...
How does Matlabs svd() function calculate the value of V?
Hi Caleb, Happy to discuss the svd with you! That being said, as others here have mentioned, svd is a building block and not e...
5 months ago | 1
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...
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...
6 months 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...
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...
7 months 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...
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...
8 months 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 ...
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 ...
8 months 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...
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...
10 months 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. ...
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. ...
10 months ago | 0
| accepted
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...
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...
10 months 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...
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...
10 months 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 ...
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 ...
10 months 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...
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...
1 year ago | 0
| accepted
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...
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...
1 year 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...
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...
1 year 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...
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...
1 year ago | 0
| accepted
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...
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...
1 year ago | 1
| accepted
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...
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...
1 year 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),...
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),...
1 year 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...
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...
1 year 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...
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...
1 year 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...
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...
1 year ago | 0
| accepted
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...
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...
1 year ago | 0
| accepted
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...
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...
1 year 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...
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...
1 year ago | 0
