# Christine Tobler

### MathWorks

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

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**Feeds**

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...

12 days ago | 1

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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 month 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),...

1 month 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...

2 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...

2 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...

2 months ago | 0

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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...

2 months ago | 0

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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...

3 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...

3 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...

3 months ago | 1

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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...

3 months ago | 1

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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...

4 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...

5 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...

5 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...

5 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...

5 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 - ...

6 months ago | 0

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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...

6 months ago | 0

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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 ...

6 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...

7 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 ...

7 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...

7 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...

8 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...

10 months 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...

10 months 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(...

10 months ago | 0

Eigenvalues and Eigenvector computation on extremely bad conditioned matrices

If the matrix P has rank 120 and its size is 160, you should expect 40 eigenvalues to be Inf - this is how singularities in the ...

10 months ago | 0

QR factorization of a low rank matrix

Let's start with computing a rank-2 approximation of a large matrix. In general, this would be done using the SVD, but if you kn...

11 months ago | 0

Can additional information be added to the directed graph plotting node 'tooltip'?

Yes, you can do this using the dataTipTextRow function: nodeNames = {'Node A', 'Node B', 'Node C', 'Node D', 'Node E', 'Node F'...

11 months ago | 0

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computational complexity of svds

There is a recent function (introduced R2020b) called svdsketch, which is using randomized linear algebra. We recommend this for...

11 months ago | 0