Christine Tobler
MathWorks
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Graph and Network Algorithms, Linear Algebra, Quantum Computing
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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...
14 dagen ago | 1
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...
23 dagen ago | 0
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 maanden ago | 0
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 maanden ago | 0
| accepted
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 maanden ago | 10
| accepted
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 maanden ago | 0
| accepted
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?
5 maanden ago | 0
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 maanden ago | 1
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 maanden ago | 1
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 maanden ago | 1
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 maanden ago | 0
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 maanden ago | 3
| accepted
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 maanden ago | 0
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 maanden ago | 0
| accepted
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 maanden ago | 0
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 maanden ago | 0
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 maanden ago | 0
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...
ongeveer een jaar ago | 0
| accepted
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...
ongeveer een jaar ago | 0
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...
ongeveer een jaar ago | 0
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...
ongeveer een jaar ago | 0
| accepted
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...
meer dan een jaar ago | 1
| accepted
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...
meer dan een jaar ago | 1
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),...
meer dan een jaar ago | 2
| accepted
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...
meer dan een jaar ago | 1
| accepted
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...
meer dan een jaar ago | 0
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...
meer dan een jaar ago | 0
| accepted
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...
meer dan een jaar ago | 0
| accepted
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...
meer dan een jaar ago | 0
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...
meer dan een jaar ago | 0
