Glas List: Re: [glas] dotc and dotu in glas

From: Sanz, Christophe (Christophe.Sanz_at_[hidden])
Date: 2006-05-02 05:27:23

Quoting Karl Meerbergen <Karl.Meerbergen_at_[hidden]>:

> Removing ambiguity is a strong argument for having two different
> functions, dotc() and dotu().
>
> Karl
>
Do you mean that there is no interest for a GLAS to define a proper
specialisation of the dot function for a collection of values with complex
types, which specialisation could co-exist with both dotu & dotc?

>
>
> Sanz, Christophe wrote:
>
> >Quoting Karl Meerbergen <Karl.Meerbergen_at_[hidden]>:
> >
> >
> >
> >>As far as I understand, Toon was talking about core syntax, not
> >>functionality:
> >>is there a  problem with dot(conj(x),y) for the euclidean inner product?
> >>
> >>Karl
> >>
> >>
> >>
> >
> >Possibly not but there seem to remain some ambiguity pertaining to the
> choice of
> >the proper specialisation of the dot function for collection of complex
> types.
> >The maths would suggest that it is dotc while (eg:) the MTL would suggest
> that
> >it is dotu. Possibly the latter option was just too straightforward to be
> >avoided in first place but retaining option 1 could be well worth a
> >confirmation. Was that Matthias meant?
> >
> >
> >>Matthias Troyer wrote:
> >>
> >>
> >>
> >>>I want to strongly support Andrew's statement. If one wants only one
> >>>dot product then the proper inner product for a complex Hilbert space
> >>>needs to be chosen.
> >>>
> >>>Matthias
> >>>
> >>>On May 1, 2006, at 10:59 AM, Andrew Lumsdaine wrote:
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>>Both are needed.
> >>>>
> >>>>In the Iterative Template Library, both are required in order for the
> >>>>solvers to work properly with complex vectors.
> >>>>
> >>>>Mathematically, dotc() is a proper inner product for a complex Hilbert
> >>>>space, dotu() is not.  If a single dot() function is going to be used
> >>>>for inner product, mathematically it must be equivalent to dotc().
> >>>>
> >>>>Use cases are very important when creating interfaces for a generic
> >>>>library.  I would suggest taking a look at ITL and IETL to see how
> >>>>generic linear concepts at this level of abstraction are used.
> >>>>
> >>>>Toon Knapen wrote:
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>>I was wondering if we need an equivalent for both the dotc and
> >>>>>dotu of
> >>>>>BLAS in glas? I suggest to only have _one_ dot function (which is
> >>>>>equivalent to the dot in blas for vectors of reals and which
> >>>>>corresponds
> >>>>>to dotu for vectors of complex values). To perform the equivalent of
> >>>>>dotc one could then write dot(conj(x),y). This is IMHO clearer and
> >>>>>the
> >>>>>expression-template mechanism will avoid that this compound
> >>>>>expression
> >>>>>will induce a performance penalty.
> >>>>>
> >>>>>I just added an equivalent to dotc but I plan to add the solution as
> >>>>>described above, benchmark both and than remove the dotc equivalent
> >>>>>afterwards (supposing the benchmark will not show any performance
> >>>>>differences of both approaches).
> >>>>>
> >>>>>toon
> >>>>>
> >>>>>
> >>>>>_______________________________________________
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> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>_______________________________________________
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> >>>>
> >>>>
> >>>>
> >>>>
> >>>_______________________________________________
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> >>>
> >>>
> >>>
> >>>
> >>>
> >>--
> >>==============================================
> >>Karl Meerbergen
> >>
> >>Free Field Technologies
> >>
> >>NEW ADDRESS FROM FEBRUARY 1st ONWARD:
> >>
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> >>rue Emile Francqui, 1
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> >>
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> >>============================================
> >>
> >>
> >>
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> >>
> >>
> >>
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> >
> >
> >
>
>
> --
> ==============================================
> Karl Meerbergen
>
> Free Field Technologies
>
> NEW ADDRESS FROM FEBRUARY 1st ONWARD:
>
> Axis Park Louvain-la-Neuve
> rue Emile Francqui, 1
> B-1435 Mont-Saint Guibert - BELGIUM
>
> Company Phone:  [phone]
> Company Fax:    [phone]
> Mobile Phone:   [phone]
> Home Phone:     [phone]
> mailto:Karl.Meerbergen_at_[hidden]
> http://www.fft.be
> ============================================
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