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Subject: Re: FEM substructuring  (static condensation) -> out ot memory; ANSYS can do it
Date: Sun, 1 Jun 2008 11:50:02 +0000 (UTC)
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> what are the dimensions of these matrices?  Kbb is dimension
> 5000?
> 
> What's happening here is that you're computing your own
> Schur complement.  It might be too much to represent this
> explicitly.  Perhaps ANSYS does this implicitly, and
> updates/downdates the factorization of K accordingly.
> 
> MATLAB uses the same compressed-sparse column form that the
> Harwell-Boeing format uses (mostly, except for different
> methods used inside LU, Chol, backslash, etc, that aren't
> visible to the user - M or mex or otherwise).
> 

Hi Tim,

Kbb could be larger than 5000, but 5000 is approximately the
dimension where I get problems with MATLAB running out of
memory.

How would I calculate the Schur Complement implicitly? Is
there a special algorithm I could look up, or is an implicit
calculation of the Schur complement included in Matlab?

Thanks

Btw.

Nice book you wrote about sparse linear systems. I have to
admit I got lost pretty soon, as I'm only a mechanical
engineer and never learnt graphs, but it helped me a lot to
speed up my code for creating large sparse matrices.