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Re: [glas] dotc and dotu in glas

From: Matthias Troyer (troyer_at_[hidden])
Date: 2006-05-01 15:25:50

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.


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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