Drexel dragonThe Math ForumDonate to the Math Forum



Search All of the Math Forum:

Views expressed in these public forums are not endorsed by Drexel University or The Math Forum.


Math Forum » Discussions » Software » comp.soft-sys.matlab

Topic: Solving sparse Ax=b without certain eigenvector spaces
Replies: 11   Last Post: Aug 8, 2014 3:25 AM

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View   Messages: [ Previous | Next ]
John D'Errico

Posts: 9,060
Registered: 12/7/04
Re: Solving sparse Ax=b without certain eigenvector spaces
Posted: Aug 2, 2014 8:37 PM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

"Hui " <huiprobable@gmail.com> wrote in message <lrjnpr$klo$1@newscl01ah.mathworks.com>...
> Hi, I'm trying to solve a sparse Ax=b problem. The size of A is about 10^4 by 10^4. A is pretty singular and the first a few eigenvalues of A is about 10^(-12), 10^(-6) and 10^(-4). I'm able to find the first a few eigenvalues and eigenvectors using the command eigs, which takes only one or two seconds. Now I want to find x, such that Ax=b, but I want to exclude the first three eigenvectors.
>
> Are there any simple ways that allow me to do this?


Pretty singular? Excluding eigenvectors? Please define your terms,
as pretty singular does not have a clear definition.

I'm also perplexed by your statement that the first eigenvalue you
list is the smallest of the bunch, but also what your goals are here.

My guess is you wish to deflate the matrix, removing those first few
eigen-components from A.

john



Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© Drexel University 1994-2014. All Rights Reserved.
The Math Forum is a research and educational enterprise of the Drexel University School of Education.