Christine Tobler

Last seen: 1 día ago

MathWorks

293 total contributions since 2015

Professional Interests: numerical linear algebra, graph algorithms

Christine Tobler's Badges

Answered
Direct Solver
The direct sparse solver (\) unfortunately doesn't have methods for complex symmetric or hermitian problems, only for real symme...

2 días ago | 0

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Solve large linear equations with backslash operator. Why is sparse matrix solved slower than the full matrix?
Sparse linear system solvers are usually fast for sparse matrices with specific structure of where the nonzeros are placed. For ...

6 días ago | 0

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EIGS: Why is 'smallestabs' faster than 'largestabs'?
Whether 'largestabs' or 'smallestabs' depends on the problem: 'smallestabs' needs to factorize the first input, which can make i...

9 días ago | 0

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What is the algorithm used by svd function?
We don't give information on what SVD algorithm we use, look up the LAPACK library for detailed descriptions. For practical pur...

10 días ago | 1

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Inverse of higher order matrix
Another way of looking at the equations x*Q = 0 and x e = 1 is as an equation system x * [Q e] = [0 1], which you could solve us...

18 días ago | 0

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How to decompose a 4th order tensor
The value of K1111 is overwritten with the next value in every loop iteration - is this your intention, or did you maybe mean to...

25 días ago | 0

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How can I find the Members of the largest component of a graph?
Use oF = F_prime.Nodes.Name(bin==m); instead of the find command to return node names instead of node numbers.

30 días ago | 1

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Projecting data points onto eigenvector space
The lambda here is a diagonal matrix, so SORT will sort each of its columns, not the eigenvalues on the diagonal among themselve...

alrededor de 1 mes ago | 0

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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...

alrededor de 1 mes 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...

alrededor de 1 mes 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...

alrededor de 1 mes 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...

alrededor de 1 mes 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...

alrededor de 1 mes 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...

alrededor de 1 mes 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.

alrededor de 1 mes ago | 0

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Answered
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...

alrededor de 2 meses 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...

alrededor de 2 meses 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...

alrededor de 2 meses ago | 0

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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...

alrededor de 2 meses ago | 0

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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 ...

3 meses ago | 2

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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;...

3 meses 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...

3 meses ago | 1

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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...

3 meses ago | 0

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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...

3 meses ago | 0

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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:

3 meses ago | 1

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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...

3 meses 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...

4 meses 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...

4 meses 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...

4 meses 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...

4 meses ago | 0