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Christine Tobler


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MathWorks

285 total contributions since 2015

Professional Interests: numerical linear algebra, graph algorithms

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Answered
Soring varying and compex eigenvalues
This can't be done one the level of individual EIG calls, since it's necessary to track eigenvalues from one call to the next. T...

2 days ago | 0

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Change position of Graph edge label and node label
The position of the labels that are part of the graph plot can't be modified. It's possible to create independent text labels an...

7 days ago | 0

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Specifying node numbers using digraph
The easiest way to use graph/digraph when your node numbers are not sequential is to convert the node numbers to string, which w...

7 days ago | 0

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Cannot create a matrix using pinv.
You've hit on a rare matrix that the SVD algorithm isn't able to work with (the SVD being the factorization called withing the P...

8 days ago | 0

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Solving for ALL the eigenvectors of a sparse matrix
There isn't really an algorithm like this, unless you have a very specific structure (tridiagonal or banded matrix mostly). The...

8 days ago | 1

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How to add an edge between two nodes of two different graphs?
You could also add the edges of both graphs to one larger graph, and then use addedge to connect them. You would probably not ge...

9 days ago | 1

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How to make nodes' removal from a graph as a function of time?
You may want to look at the graph and digraph classes: Graph and Network Algorithms and their method rmnode specifically.

13 days ago | 0

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How to determine if a graph is two-connected?
The biconncomp function will split the edges of a graph into its biconnected components. If the output of biconncomp is a vector...

16 days ago | 0

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Computing generalized Inverse of a square but sparse matrix?
If you want to apply pinv(A)*b, you can instead use lsqminnorm(A, b), which also works for sparse matrices and does something eq...

19 days ago | 0

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Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 9.735910e-18.
I tried plotting the following two things: >> figure; semilogy(max(abs(A), [], 1)) >> figure; semilogy(max(abs(A), [], 2)) Fr...

19 days ago | 0

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Answered
Modify Nodes and Edges of GraphPlot
I'm afraid that's not possible with GraphPlot. For performance, you could use scatter to plot all the nodes, and plot to plot a...

19 days ago | 0

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Answered
how to find out the common neighbors of two nodes in a graph?
You can use the graph class for something like this. First, make a graph from the connection inputs you had: >> A=[1 2; 1 3; 1 ...

2 months ago | 2

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Answered
Error using tabular/permute and Error in median (line 186)
Applying median to a table directly is not supported. Either apply median to a specific variable of the table >> t = table([3;...

2 months ago | 0

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Finding bridge of not isolated vertices
There is no functionality for MATLAB's graph class that would compute the bridges / cut edges. If performance is not a main con...

2 months ago | 1

Answered
How do I stop incidence function rearranging the edges of a graph?
The reordering isn't happening when the incidence of the graph is computed, but instead at the moment that the graph is construc...

2 months ago | 0

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Answered
Generalized Eigenvalue Problem - Hessenberg Matrix
I agree with Steve Lord; if you're able to replicate the action of matrix A on a vector v, you can pass this to EIGS in a functi...

2 months ago | 0

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Answered
Generating all non-isomorphic graphs for a given number of nodes with specified degrees
I've attached a script that computes the graphs in your example, here's the plot of all graphs it found:

2 months ago | 1

Answered
how to find kshortest path or use Dijkstra algorithm for 12 plot points.
I'm not sure how the data you're adding here maps to the picture you attached. Here's how I would go about inserting the positio...

2 months ago | 0

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generate multi Diagonal matrices
The SVD is usually computed for a matrix, but you're only passing in a scalar on each call. Is it possible you meant to pass in...

3 months ago | 0

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S is diagonal matrix of singular values?
MATLAB (and Fortran) store matrices in a column-first ordering, while in your file, you want to save numbers in a row-first orde...

3 months ago | 0

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Answered
Performance of matlab direct linear solver with respect to sparsity
For sparse matrices, the performance of backslash depends a lot on the specific structure of that sparse matrices (where the non...

3 months ago | 0

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Answered
How can I return real-valued eigenvectors from diagonalization?
I don't think it's possible: Looking at the eigenvalues and eigenvectors of B, >> diag(D) ans = 0.0000 + 2.0000i 0.000...

3 months ago | 0

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incorrect eigenvector using eig(A,B)
The residual MK*V-MM*V*w2 is expected to be numerically close to zero, however, you have to take into account the scaling of the...

3 months ago | 0

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highlight Nodecolor for a graph using a color map (JET)
Since colors is a n-by-3 array, use colors(i, :) to access the complete row that represents the color for node i. You can also u...

4 months ago | 0

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Answered
Path between 2 nodes in a graph
Compute a path between the nodes, then check if the result is empty (this is returned by shortestpath if no path exists): path ...

4 months ago | 1

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Diagonalising a Skew-Symmetric Matrix
When EIG is called with an exactly symmetric/hermitian matrix, MATLAB falls back to a specialized algorithm that guarantees that...

4 months ago | 2

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Answered
Properties of SVD of a hermitian matrix not holding at single precision
I'd suggest just calling EIG [V, S] = eig(A) instead of calling the SVD. If A is (exactly!) symmetric on input, this will retu...

4 months ago | 0

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Answered
What is the difference between Gram-Smith QR decomposition procedure and qr.m function in Matlab?
MATLAB's QR decomposition is computed using Householder transformations, which is generally more numerically advantageous.

4 months ago | 0

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Answered
Plotting a graph in layered fashion
Unfortunately, there is currently no way to do this with the 'layered' layout. I'll make a note of your need for this. For now,...

4 months ago | 0

Answered
Shortest path through nodes
As Bjorn mentioned, this is the traveling salesman problem. The optimization toolbox has an example of how to use their intlinpr...

5 months ago | 1

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