[CIG-SEISMO] Mineos problem

[Matthew Knepley]

On Thu, Mar 3, 2016 at 10:30 AM, Andrew Valentine <a.p.valentine at uu.nl>
wrote:

> Hi all,
>
> There are known problems with Mineos, which is built around various early
> (and somewhat bespoke) numerical routines. Unfortunately computing
> eigenfunctions and eigenfrequencies of earth models is somewhat complex,
> and it isn’t as simple as switching to a modern Lapack solver. Work is in
> progress to implement a replacement for Mineos (see, e.g.,
> http://www.geo.uu.nl/~andrew/talks/talk_egu2015.pdf), but this is not
> ready yet.
>

I read the talk. It seems to ignore all the work done on the numerical
eigenproblem since 1970. Why would you not just
use one of the many freely available solvers instead of solving the secular
equation?


> I think there are some posts from Martin van Driel in the archive of this
> mailing list that describe some of the problems in more detail.
>

Are these archives searchable? The link from the Mineos webpage does not
incorporate a search.

  Thanks,

     Matt


> A number of the numerical issues can be reduced - but not completely
> eliminated - by generating a 1D model input file that has a finer grid
> spacing. (The versions of PREM distributed with Mineos are sampled on 185
> knots, but it is straightforward to create versions with a higher number of
> samples.) This tends to improve the integration stability, and also reduces
> errors that arise during normalisation of eigenfunctions. If it is desired
> to increase the number of knots by more than a modest amount, it will be
> necessary to increase the size of the arrays Mineos uses as memory buffers.
>
> All the best,
> Andrew
>
>
>
>
> > On 03 Mar 2016, at 16:00, Matthew Knepley <knepley at rice.edu> wrote:
> >
> > We have a problem with the eigenfunctions calculated by Mineos at near
> degenerate eigenvalues.
> >
> > Mineos works fine to calculate the eigenfrequencies of normal modes, but
> there is a problem for the eigenfunctions. For those different modes with
> very close eigenfrequencies in the mathematical point of view(see Figure
> f-l), Mineos regards them as degeneracy in the numerical point of view, and
> therefore it gets a linear combination of pure R mode's and pure Stoneley
> mode's eigenfunctions, i.e. the eigenfunctions are not orthogonalized. For
> example, based on Okal's classification [1], 2S25  and 3S25 should be
> Stoneley mode and R mode, respectively. But the eigenfunctions from Mineos
> have both surface oscillations (the feature of R modes) and exponentially
> decaying along CMB (the feature of Stoneley modes).(see Figure 2S25 and
> 3S25)
> >
> > Since the eigenfunction is not calculated properly, the group velocity
> is also not reliable. According to Okal's paper [1], for each branch of R
> modes or Stoneley modes, the group velocity should be continuous. And we
> notice that there are some "bad points" in the group velocity picture,
> which are exactly the modes we mention before. (see Figure groupV_R2)
> >
> > What eigensolver is being used inside Mineos? The standard symmetric
> eigensolvers in LAPACK handle this problem I believe.
> >
> >   Thanks,
> >
> >     Jingchen and Matt
> >
> > References:
> >
> > [1] Okal, Emile A. "A physical classification of the earth's spheroidal
> modes." Journal of Physics of the Earth 26.1 (1978): 75-103.
> >
> > _______________________________________________
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> > CIG-SEISMO at geodynamics.org
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>
> --
> Dr Andrew Valentine
> Postdoctoral Researcher
>
> Department of Earth Sciences, Universiteit Utrecht
> Postbus 80.115, 3508TC Utrecht, The Netherlands
> +31 (0)30 253 5192  -  www.geo.uu.nl/~andrew
>
>
>
>
>
>
>
>
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