# Christine Tobler

### MathWorks

Professional Interests: numerical linear algebra, graph algorithms

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**Content Feed**

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...

14 days ago | 2

| accepted

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...

20 days ago | 0

| accepted

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...

1 month ago | 2

| accepted

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...

1 month ago | 0

| accepted

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...

1 month ago | 0

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 ...

2 months ago | 1

| accepted

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...

2 months ago | 1

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...

2 months ago | 2

| accepted

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...

2 months ago | 1

| accepted

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...

2 months ago | 0

| accepted

How to enhance the performance of Matalb's function sqrtm?

Not in general. You might be able to find a cheaper but less accurate way to compute this, but if that's acceptable would depend...

2 months ago | 0

fastest path between more than two nodes

To compute simply the shortest-path distance, you can use the distances function and pass in a graph object you've constructed u...

2 months ago | 1

Follow a complex eigenvalue in a spectrum at different times

You could try using the matchpairs function: rng default; d = randn(20, 1) + 1i*randn(20, 1); d2 = d + 0.1*(randn(20, 1) + 1i...

2 months ago | 0

| accepted

Error using eig in Matlab 2021b by using Parallels 17 of Macbook Pro (M1 )

Since MATLAB is trying to load a .dll file, I'm assuming you're running a Windows VM on this Macbook Pro. MATLAB doesn't support...

3 months ago | 0

use of svds with function handles

The svds function needs to be able to apply both A*x and A'*x, so your function handle should accept a second input which is eit...

3 months ago | 2

How to compute cholesky to all slice of a tensor?

There isn't another way to do this right now. We have functions that do other linear algebra operations to each page of an ND-ar...

3 months ago | 1

Why does mldivide solve equations so fast that FORTRAN can't compare it？

MATLAB's mldivide uses multithreading. It doesn't use the GPU unless you have the Parallel Computing Toolbox and are using the g...

3 months ago | 0

How to highlight single edges in an undirected graph?

Do you still want the multiple edges to be displayed? If not, you can use the simplify command to reduce all multiple edges to j...

4 months ago | 1

| accepted

Unable to find out left eigen vectors of symbolic matrix

The left eigenvectors are still expressed as right eigenvectors of M', meaning they satisfy a slightly different equation: syms...

4 months ago | 0

| accepted

Program to find connected and non-isomorphic graphs

In the last loop, you are checking if adj is isomorphic to any previous graph. If there is one graph that adj is not isomorphic ...

4 months ago | 0

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How can I invert a big matrix e.g. 1000-by-1000

When running inv on this matrix, there's a warning: >> M = inv(current_Fit_Mat); Warning: Matrix is close to singular or badly...

5 months ago | 0

Add an automatic TOC to an .mlx

You can go the "Insert" tab (just to the right of where it says "Live Editor" on top of the MATLAB window) and there's a button ...

5 months ago | 0

How to get a Table Contents in Live Script .mlx export to HTLM

You can go the "Insert" tab (just to the right of where it says "Live Editor" on top of the MATLAB window) and there's a button ...

5 months ago | 0

How is SVDS execution time related to the target rank?

So the goal of svds is usually to compute a requested rank that is much smaller than either size of the input matrix. A search s...

5 months ago | 0

| accepted

How to solve eigs/checkInputs issue in EOF analysis?

The error here is happening because R eof>mycaleof is an empty matrix, and eof is trying to compute an eigenvalue of it. Looking...

5 months ago | 0

How to make the color in the "highlight" function stronger and well defined (not pale/transparent as by default) ?

Set h.EdgeAlpha = 1;

5 months ago | 0

| accepted

How to find out isolated subgraph?

The component output in your code is the number of components. You can use the second output of conncomp to get a vector contai...

5 months ago | 1

Find all cycles (or the initial node of each cycle) in a very large directed graph (12m nodes, 6.7m edges)

Have you tried using 'MaxNumCycles' to only compute the first 100 / 1000 / 1e4 cycles? That could give some indication if it's c...

6 months ago | 1

Finding number of independent pathways in a graph

I'd expect the call to rmedge is the most expensive here. You could instead add edge weights for every edge in the graph, and th...

7 months ago | 0

Feature for eigs involving just positive eigenvalues

There's no option to do so directly, since it's not a common request and there's already a lot of option names in EIGS to dig th...

7 months ago | 0

| accepted