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Ublas :

From: Andrew Rieck (arieck_at_[hidden])
Date: 2005-07-11 20:14:13

The following:

#include <boost/enable_if.hpp>

would provide a very clean solution for selecting specializations based on
group/ring/field/etc properties.
In this case the above library relies on the SFINAE principle.

Kind regards,

ublas-bounces_at_[hidden] wrote on 12/07/2005 09:29:46 AM:

> > The use of "abs" etc. in traits class may be worth, if you decide to
> > enable "contexts" in calls to ublas:
> >
> > May be this example is too "corner case" , but anyway :) .
> > Suppose that I have a "scalar" class C , which is internally
> > to 2x2 matrix.
> Your example reminds me of a few points I have raised before, which
> I re-state
> in a different context. If your C class is isomorphic to a 2x2 matrix,
> make it a little more concrete and consider a 2x2 matrix of double.
> You want to use C as a scalar class with uBLAS. It would not be safe to
> this if:
> 1) uBLAS assumed that every non-zero element of class C has a
> inverse. See
> Your class C would have to cope with elements of C which do not have an
> inverse. Maybe it would return a NaN result, or throw an exception when
> for 1/c, where c is in C and c has no inverse. Then uBLAS would have to
> with NaN (or an exception) as a result of 1/c.
> 2) uBLAS assumed that multiplication is commutative.
> See
> If you hand uBLAS two scalars, a and b of type C, where a*b != b*a, then
> would want to be sure that there are no places in uBLAS which assume
> a*b == b*a.
> Then again, maybe either or both of these assumptions allow some
> optimization somewhere in uBLAS. In this case, you would want uBLAS to
> provide some sort of ring_traits, such as is_division_ring<T>,
> is_commutative_ring<T>. Then uBLAS would be able to have different code
> the different cases, allowing both correct operation and optimization
> possible.
> The same ideas apply to the other field and ring axioms, although I
> personally draw the line at addition. AFAICT, it is reasonable to assume
> any scalar class K used with addition in uBLAS would be such that K
models an
> Abelian group under addition (possibly subject to IEEE arithmetic and
> rounding error).
> Maybe the best idea would be to assume that any scalar class K which is
> with the algebraic operations of uBLAS would be such that K models a
> and then supply ring_traits to cover the extra axioms between ring and
> See

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