Re: EigenSystem fails to converge
- To: mathgroup at smc.vnet.net
- Subject: [mg93897] Re: EigenSystem fails to converge
- From: dh <dh at metrohm.com>
- Date: Fri, 28 Nov 2008 05:06:42 -0500 (EST)
- References: <gglsn9$8at$1@smc.vnet.net>
Hi Adel,
from the Help in version 7 under "Possible Issues":
"You can use method options with Method -> {Arnoldi, opts} to \
increase the basis size or the maximum number of iterations, reduce \
the tolerance, or use an estimate as a shift, any of which may help."
and:
"You can give the algorithm a shift near the expected value to speed up
convergence:
{vals, vecs} =
Eigensystem[s, 3, Method -> {"Arnoldi", Shift -> -4}]; ListPlot[vecs,
PlotLabel -> vals]"
hope this helps, Daniel
Adel Elsabbagh wrote:
> Dear Mathematica professionals,
>
> I have a system which I am trying to find its N lowest eigenvalues and
> vectors using the function:
> [l,u] = EigenSystem[{K,M},-N];
> K and M are quite large matrices in the order of 1000*1000, and whose
> entries are complex numbers.
> The Eigensystem function works fine most of the time. However, sometimes it
> gives me the following error for no reason that I know:
> Eigensystem::cfail : Algorithm failed to converge.
>
> Are there any options/methods for Eigensystem that I can choose and which
> will allow the convergence?
>
> Kind regards,
>