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Christine Tobler

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Answered
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...

1 day ago | 0

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Answered
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...

1 day 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; ...

4 days ago | 0

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Answered
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.

9 days ago | 0

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Answered
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...

9 days ago | 0

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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...

13 days ago | 0

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Answered
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...

14 days 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...

14 days ago | 1

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Answered
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...

20 days ago | 1

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Answered
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...

27 days ago | 0

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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...

1 month ago | 1

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Answered
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...

1 month ago | 2

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Answered
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...

2 months ago | 0

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Answered
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 ...

2 months ago | 0

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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:...

2 months ago | 1

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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 ...

2 months ago | 1

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Answered
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. ...

2 months ago | 1

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Answered
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...

3 months ago | 0

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Answered
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...

3 months ago | 1

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Answered
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...

4 months ago | 1

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Answered
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...

4 months ago | 2

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Answered
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...

4 months ago | 0

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Answered
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...

5 months ago | 3

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Answered
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...

5 months ago | 0

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Answered
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...

5 months ago | 0

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Different results on different computers, Matlab 2021b - 64 bit, windows 64 bit, both Intel chips
First, about "which value to trust?" Both values are equally trustworthy, the differences in results come down to applying the ...

5 months ago | 1

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Answered
eigs with Extended Capabilities
The first of these would only be useful if you need to apply EIGS to many problems in parallel, in which case each of these coul...

5 months ago | 1

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How to parallelize many small SVD's on a GPU
As of R2021b, there is a function pagesvd which is supported on both CPU and distributed arrays. It's not supported for gpuArray...

5 months ago | 2

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Answered
How does shortestpath function work?
Every edge has a number, which is the order in which they appear in the Edges table (try displaying g.Edges). The edgepath conta...

5 months ago | 1

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Answered
Eigs passes the wrong StartVector
The standard method used in EIGS is only efficient for matrices that are quite large. When eigs detects that the input matrix is...

6 months ago | 0

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