# Christine Tobler

### MathWorks

Professional Interests: numerical linear algebra, graph algorithms

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**Content Feed**

GUI crashes when using eigs with a nonzero shift on a large generalised eigenvalue problem.

Ideally this shouldn't crash, but produce an out-of-memory error. However, for example on Linux there is the "out-of-memory kill...

8 days ago | 0

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GPU speed up for pcg() is disappointing

It looks like you can simply replace your current call to pcg with x = pcg(A, b, tol, 5000, @(y) L\y, @(y)L'\y); as the error ...

23 days ago | 0

What is matlab doing under the hood when I solve this generalized eigenvalue problem?

You can use the Display option to get some more information on what's going on inside of eigs. load matrices.mat [V,D] = eigs(...

28 days ago | 1

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Trapz error in calculating 2D integrals: ORDER contains an invalid permutation index

Replace the line I = cumtrapz(y,cumtrapz(x,MBerry(keySet),2)); with I = cumtrapz(y,cumtrapz(x,MBerry(keySet),2), 1); Here'...

1 month ago | 0

`svd` sometimes blows up - how to fix it?

In short, the problem is that pinv_modified is based on a misunderstanding of the workaround here. The idea is to check if SVD f...

2 months ago | 1

Calculating node coordinates for a graph without plot command

Unfortunately there isn't a way to get these coordinates without plotting. I have added your request for such a function to our ...

2 months ago | 1

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'MarkerEdgeColor' for Graph/Digraph Nodes

Yes, MATLAB's graph and digraph plots only have one NodeColor property which applies to both the marker's FaceColor and EdgeColo...

2 months ago | 0

How to convert a graph / edges list into a shapefile (.shp) ?

There isn't a direct way to do this with a graph object. The mapping toolbox has a shapewrite function which produces a .shp fil...

3 months ago | 0

Condition number of empty matrix

The case of a 0-by-0 matrix doesn't have any very useful definition, as you note correctly in the comments above. MATLAB does w...

3 months ago | 1

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How to fix **Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 1.053110e-20.** ?

Yes, the matrix A becomes singular after applying the last two for-loops (which I think are the boundary conditions). You can v...

4 months ago | 1

How to check if there is an edge between two nodes in an undirected graph?

Call findedge(g, node1, node2). If there is no edge connecting these nodes, the output is zero. Otherwise, the output is the ind...

5 months ago | 0

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Why does lu function yield different lower triangle matrix if I return [L,U] rather than [L, U, P]?

The LU decomposition really involves three new matrices: An upper-triangular matrix U, a lower-triangular matrix L, and a permut...

5 months ago | 0

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How to find a permutation matrix to turn a general hermitian matrix into a block diagonal one?

First, we should keep in mind that the task is really to find a representation of A with as small blocks on the diagonal as poss...

5 months ago | 0

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Interpreting eigenvalues and eigenvectors when using symbolic toolbox

I'm getting both 4 eigenvalues and 4 eigenvectors when running your code: linkMatrix = [0,1/3,1/3,1/3; 0,0,1,0; ...

5 months ago | 0

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Different behaviour in indexing between table and digraph node table

This is a bug in digraph, thank you for reporting it! I have passed it along and it will be fixed in a future release.

5 months ago | 0

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Linking nodes using links in a graph based on information from another layer

You could represent the first layer as a graph object, adding coordinate information for each node to the Nodes table. For the s...

5 months ago | 0

Error message when trying to compute EOF with covariance matrix.

The problem is that the covariance matrix becomes very large here. Luckily, it's not necessary to compute this matrix explicitly...

5 months ago | 0

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Sorting eigenvectors using symbolic toolbox for PageRank algorithm

There's an unknown variable in the value you pass to sort, so this won't be sorted by magnitude as the magnitude isn't known. H...

5 months ago | 0

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eigenvalue and eigenvector of free vibration while stiffness matrix is not invertable

If eig has been working well for the size of your problem you could consider using [U, D] = eig(K, M); %this solves K*U = M*U*D...

5 months ago | 1

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Finding a node in graph with most mutually adjacent nodes

Thanks for adding the tag, Steve! Here's another idea for how to do this. So you want to find all pairs of edges that go a->b a...

5 months ago | 1

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eigen value what i am getting from matlab software that is not exact when i am compairing with hand calculated value and the mode shape i am getting is reverse

The results look correct to me, can you say what you are expecting instead? Two points that are maybe relevant: MATLAB does num...

6 months ago | 0

The node number in the digraph does not match the node number used in shortestpath().

Try putting the node numbers in quotes: [path,d, edgepath] = shortestpath(G,"228","231"); You have given each node a name, and...

6 months ago | 1

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Unitary matrix with non-orthogonal eigenvectors?

The short answer is that it's possible to compute an orthonormal basis of eigenvectors for an orthogonal matrix, but that MATLAB...

6 months ago | 2

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Eigenvalue problem on non-Hermitian matrix

You can think of it like this: If there is an invertible V such that inv(V)*H*V=D, then you can expect that the matrix myW = inv...

6 months ago | 0

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Seasonal Breakdown from a Time Series data

Perhaps the trenddecomp function would be useful? It has an optional input period where a vector of several periods can also be ...

6 months ago | 0

How to find all the downstream nodes from a node in a graph?

Looking at this again due to the recent comment added, it might be simpler to use a directed graph instead of an undirected one:...

7 months ago | 1

Which solver should I use to solve a square and symmetric, linear system of equations?

The first thing to check is the size and density of your matrix. The SYMMLQ function you mentioned is one of a group of methods ...

7 months ago | 1

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Can we compute the graph Laplacian matrix for a directed graph?

It depends how you want to define it, there is no one consistent definition of what the graph laplacian of a directed graph is. ...

7 months ago | 1

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eigs using 'smallestabs' vs scalar

Hi Jack, I had initially misunderstood that you were getting different results when passing in 'smallestabs' vs. passing in the...

8 months ago | 0

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missing eigenvector when using eig on defective matrix

The short answer is that this is a case where a small change in the input matrix has a large effect on the eigenvectors being co...

8 months ago | 1

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