# Christine Tobler

### MathWorks

Professional Interests: numerical linear algebra, graph algorithms

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**Content Feed**

Issues with the normalisation of mode shapes?

eig(A, B) normalizes the eigenvectors in the B-mass norm, but only if it recognizes the input as a symmetric problem (A is symme...

circa un mese fa | 0

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Proof of relation between the generalized singular values of gsvd(A,B) and gsvd(B,A)

The background for this is the 5-output form of the GSVD: [U,V,X,C,S] = gsvd(A,B) returns unitary matrices U and V, a (usually)...

circa 2 mesi fa | 0

Update a sparse matrix efficiently

The fastest way to construct a sparse matrix will be when the inputs are sorted, first by columns and then by rows. You can veri...

2 mesi fa | 0

Given a big square matrix and some eigenvalues, how to find the corresponding eigenvectors?

I wouldn't expect a 3072-by-3072 matrix to be a problem on the machine you describe. Could you try to run the following on your ...

3 mesi fa | 0

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new interface for QR decomposition in Matlab 2022a

Yes, we made this change for R2022a. I'm sorry this has caused problems for you, @Klaus Diepold, could you share how you had bee...

4 mesi fa | 1

how to find eigenvalues using the determinant ?

The determinant should only be used explicitly to solve an eigenvalue problem for symbolic calculation (for example, when you so...

4 mesi fa | 2

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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...

6 mesi fa | 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 ...

6 mesi fa | 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(...

7 mesi fa | 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'...

7 mesi fa | 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...

8 mesi fa | 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 ...

8 mesi fa | 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...

8 mesi fa | 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...

9 mesi fa | 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...

9 mesi fa | 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...

10 mesi fa | 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...

10 mesi fa | 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...

10 mesi fa | 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...

10 mesi fa | 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; ...

10 mesi fa | 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.

11 mesi fa | 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...

11 mesi fa | 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...

11 mesi fa | 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...

11 mesi fa | 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...

11 mesi fa | 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...

11 mesi fa | 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...

11 mesi fa | 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...

12 mesi fa | 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...

12 mesi fa | 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...

12 mesi fa | 0

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