# Christine Tobler

### MathWorks

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Graph and Network Algorithms, Linear Algebra, Quantum Computing, Automatic Differentiation

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**Feeds**

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 month 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...

2 months 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...

2 months 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...

3 months ago | 0

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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...

4 months 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...

4 months 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),...

5 months 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...

5 months 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...

5 months 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...

5 months 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...

6 months 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...

6 months 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...

6 months ago | 0

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...

7 months ago | 1

| accepted

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...

7 months ago | 1

| accepted

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...

7 months ago | 0

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...

8 months ago | 2

| accepted

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...

8 months ago | 0

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...

8 months ago | 0

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...

9 months ago | 0

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 - ...

9 months ago | 0

| accepted

Trying to construct a filtered graph using pmfg function that uses the (MATLAB-BGL) library in MacBook.

The problem seems to be with the MatlabBGL FileExchange package and specifically with the .mex files that are being provided the...

9 months ago | 0

| accepted

Can I get all of the shortest paths between all pairs of nodes in a Directed Graph in one function call

Using shortestpathtree in a loop over the starting node is the way to go. You can change the data format of the first output by ...

10 months ago | 1

Inconsistency between Matlab eig() function and Matlab generated C code eig() function

For code generation, the eig function doesn't have as many special-case treatments as the eig function in regular MATLAB. This m...

10 months ago | 2

| accepted

How to control the curvature of each edge when drawing graph object?

The curvature of the edges in this plot aren't controllable. You could turn off the edges from the graph plot, and use the plot ...

10 months ago | 1

eigs function works slowly

A possible issue is that "largestreal" option works less towards the strengths of the EIGS algorithm than the default "largestab...

10 months ago | 0

Why is my parfor loop running slower than a regular for loop

The problem is likely that the cost of each iteration is still too small to warrant the start-up time of the parfor loop. You c...

11 months ago | 0

Quick method in solving symmetric linear equation

You can definitely use iterative methods such as pcg. The success of this usually depends on how well-conditioned your matrix is...

1 year ago | 1

doc QR decomposition error

Hi, As you can see here, R is an m by n matrix and Q is an m by m matrix in the default behavior of the qr function: A = randn...

1 year ago | 0

Replacing old version graphshortestpath with new shortestpath function

You can replace [ dist,path{1} ] = graphshortestpath( adjMatrix, 1, numel(newImg(:))); with [ path{1}, dist ] = shortestpath(...

1 year ago | 0