Re: Calculating eigenvector for zero eigenvalue
- To: mathgroup@smc.vnet.net
- Subject: [mg12183] Re: [mg12140] Calculating eigenvector for zero eigenvalue
- From: Daniel Lichtblau <danl@wolfram.com>
- Date: Fri, 1 May 1998 03:08:35 -0400
- References: <199804270546.BAA09532@smc.vnet.net.>
134677.95@swan.ac.uk wrote: > > I am trying to calculate the eigenvector when the eigenvalue is zero for > a 9x9 matrix. > > Using 'Eigenvalues' gives me several answers including zero, but also > some complex numbers. When I try using 'Eigenvectors' it trys to > compute the eigenvectors for all of the eigenvalues. Unfortunatly the > it seems that it can not calculate the eigenvectors for the complex > numbers and fails to provide an answer (it just runs for hours without > any output). > > Does anybody know how I can calculate just the eigenvector corresponding > to the zero eigenvalue? > > Thanks, > > Alastair > (I'm using Mathematica 3.0 for Win 95) Hard to say what might be the problem without seeing the input. I am guessing it is a symbolic matrix and the intermediate swell of expressions in that case can be tremendous. For your particular needs you might try using NullSpace, as that is what you are computing when you find eigenvectors for the eigenvalue zero. If you really truly are using (inexact) numeric matrices and cannot get a result for a 9x9 matrix then something is badly wrong and you should send an example to myself or tech support. Daniel Lichtblau Wolfram Research