# Christine Tobler

### MathWorks

Last seen: 3 days ago Active since 2015

Followers: 0   Following: 0

Spoken Languages:
English, French, German
Pronouns:
She/her
Professional Interests:
Graph and Network Algorithms, Linear Algebra, Quantum Computing, Automatic Differentiation

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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...

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

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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

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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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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

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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

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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