|
|
Blitz Support : |
From: Matthias Schillinger (matthias_at_[hidden])
Date: 2003-09-12 03:45:48
Hi Julian,
I've now coded a workaround for me by just overloading a new function "conj2"
for TinyVectors and complex<double> and applying a
BZ_DECLARE_FUNCTION(conj2);
to it.
Using that I can write
B=conj2(A);
whether A/B are vector or scalar fields. I just don't know if this is as good
in performance as applying std::conj directly.
What would you expect?
Regards,
Matthias
On Thursday, 11. September 2003 22:58, you wrote:
> Julian Cummings wrote:
> > Hi Matthias,
> >
> > This *should* already work, but it doesn't because of a namespace
> > problem. The standard C math functions for the blitz::Array type are
> > defined in namespace blitz, and they apply the math function to each
> > element of the Array. But they do this by calling the math function
> > with the proper namespace qualifier (usually std::). Applying
> > std::conj() to a TinyVector fails because this function is defined in
> > namespace blitz, not namespace std.
> >
> > I am not sure what is the best way to solve this problem. One
> > solution would be to invoke math functions on Array elements without
> > the std:: qualifier when defining their behavior
> > for blitz Arrays. I think this is OK because in <blitz/blitz.h> we
> > already include both <cmath> (if available) and <math.h> and then
> > import the symbols from namespace std into
> > namespace blitz. So the standard math functions should be found
> > without any qualifier.
> > I'll give this approach a try and see if it is a safe and effective
> > solution.
>
> Sadly, this approach does not seem to work. I think I looked at this
> namespace problem
> once before and wasn't able to solve it. The trouble is with the rules
> for function name
> lookup in C++. If you use non-qualified names like I was suggesting
> above, then the
> compiler will look in the current scope first, followed by any enclosing
> scopes, followed
> by the scope in which the function arguments are defined. With a using
> directive like
> "using namespace std;" you can bring function names from the std
> namespace into the
> current scope, but functions actually defined in the current scope still
> take precedence
> over the imported ones if there is a name clash. Only with a using
> declaration such as
> "using std::sqrt;" can you force the imported function to take precedence.
>
> So if you are in namespace blitz defining a standard math function like
> sqrt() acting on
> a blitz Array, you want to apply sqrt() to each Array element. If you
> apply it without
> the std:: qualifier, it will fail for built-in element types because the
> compiler tries to
> apply versions of sqrt() defined within the blitz namespace first. If
> you apply std::sqrt(),
> it will fail for TinyVector elements because that version of sqrt() is
> not in namespace std.
>
> Maybe what is needed here is a traits class to indicate if an element is
> a built-in type or not.
> I will look into this possibility ...
>
> Regards, Julian C.
-- *======================================================================* Dipl. Phys. Matthias Schillinger Institut fuer Theorie der Kondensierten Materie Tel.: +49 (721) 608-3858 E-mail: matthias_at_[hidden] *======================================================================*