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# Christine Tobler

### MathWorks

Last seen: Today Active since 2015

Professional Interests: numerical linear algebra, graph algorithms

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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...

6 dagar 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...

ungefär en månad 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...

ungefär en månad 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...

ungefär en månad 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...

ungefär en månad ago | 0

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; ...

ungefär en månad 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.

ungefär 2 månader 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...

ungefär 2 månader 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...

ungefär 2 månader 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...

ungefär 2 månader 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...

ungefär 2 månader 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...

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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...

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...

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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...

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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...

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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 ...

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:...

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 ...

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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. ...

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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...

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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...

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THE GRAPH FUNCTION DOESN'T CONSIDER WEIGHTS
Hard to say what's going wrong without seeing your code. Here's an example where you can see the weights being used to decide on...

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mldivide (backslash): advantage by using sparse matrix instead of a full matrix with respect to the quality of the results?
The condition estimate used in mldivide to decide if a warning should be given is much less accurate for the sparse case. This i...

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LDL does not support complex symmetric matrices
Largely the reason LDL doesn't support this is that it's less commonly requested for complex symmetric matrices than for complex...

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Inconsistency in behavior of SVD
Firstly, I agree completely with John's great explanations above: Any singular value below eps*first singular value should be tr...

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Accuracy Problem when solving linear equation system using: lu(S) vs. decomposition(S,'lu')
The version in decomposition does some optional steps of iterative refinement: It uses the same solution you have above based on...

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Need help fixing errors on code written in old MATLAB syntax
I'd also recommend replacing the calls svd(A) and svd(A, 0) with calling svd(A, 'econ'), since the code here is only using the f...