Re: [Lapackpp-devel] symmetry in packed storage, other questions

[Christian S. <sti...@tu...>]

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Dominik Wagenfuehr schrieb:
>> And I also cannot think of an easy solution here that would be all of
>> this: 1. easy
>> for non-mathematics, 2. give the correct results, and 3. is powerful
>> enough to actually achieve this memory optimization. Sigh.
> 
> Did you take a look at the PP-classes that means "real symmetric
> positive definite matrix stored in packed format", see
> http://docs.sun.com/source/806-7993/dpptrs.html. I haven't found a
> description what this matrices looks like but I would guess that only
> one half of the matrix is stored.

Thanks for pointing this out. The link to "dpptrs" and "dpptrf" can be
added to the documentation of LaSymmMatDouble, just for future
reference. The description of the format is in the description of the
input argument "A" and/or in the man-page of dpptrf, "man dpptrf". See
also http://www.netlib.org/lapack/lug/node121.html and its subsections
which is probably an even better explanation.

However, currently lapackpp doesn't use the "packed storage" matrix
format at all. That means none of the packed-storage LAPACK function are
declared in the C header files include/blas*.h. Obviously all the
"symmetric" classes and related LAPACK solver functions were only using
the normal storage scheme, where no storage savings were achived.

You can now either add the packed storage with its related solver
functions as an additional set of classes and functions
(LaPSymmMatDouble, for example). Or we can decide to switch the existing
symmetric classes over to packed storage. Unfortunately I have no idea
whether anyone relies on the existing symmetric classes. To be on the
safe side, I'd definitely prefer to have the packed storage as
additional classes...

Funny enough, LAPACK seems to have some more functionality for the
conventional storage than for the packed storage. For example, the
eigenvalue decompositions (dsyev,dsyevd, dsyevr, dsyevx) seems to be
unavailable for packed storage.

>> So if you're working on "dsyrk" of Blas_R1_Update, 
>> you can just as well add an alternative
>> function where the transpose setting is controlled by an additional
>> boolean argument. 
> 
> I will do so. But boolean is not enough because it could be N, T or C as
> argument.  Although I have never heard of Blas_R1_Update before I will
> use the same name and will set the last char parameter as default='N'.
> So we have backward compatibility and could use the new function. :)

What is the difference between 'T' or 'C'? I don't see any. Therefore
there are only two possibilities.

>> You're still invited to give me your sourceforge username and join the
>> lapackpp project as a developer :-)
> 
> Yes. The username is "deedw" without quotes of course. :) But I have
> never used CVS so it may be that I will send the new files to the
> mailing list.

You are added as a developer now. If the anonymous CVS access is too
slow, you can switch over to the developer access. Submitting changes by
email is still fine, though.

Christian
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