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Re: EigenSystem fails to converge

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  • Subject: [mg93897] Re: EigenSystem fails to converge
  • From: dh <dh at>
  • Date: Fri, 28 Nov 2008 05:06:42 -0500 (EST)
  • References: <gglsn9$8at$>

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."


"You can give the algorithm a shift near the expected value to speed up 


{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,


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