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Ublas : |
From: Peter Schmitteckert (peter_at_[hidden])
Date: 2007-09-20 03:57:28
Dear Ian,
Ian McCulloch wrote:
> IMHO, there is no advantage to using an unsigned int, and it is a shame
> that the STL standardized on an unsigned size_type. Unsigned has a
> positive range that is twice as big, but really, how often is that
> needed? For anything other than arrays of char, the answer is never, and
> personally I've never seen an array of char bigger than 2^31 anyway.
Well, already 2 years ago I did calcultaion (for Ingo Peschel) where I was
bounded by the 2^31 limit for diagonalizing a tridiagonal matrix in LaPack,
and had to go to long int versions.
64GB machines are more and more common, and with the switch to multi-core
we'll see more and more memory even in desktop workstations.
> The rules for mixing signed and unsigned arithmetic in C/C++ are such a
> trap that you want to avoid it, it almost never gives what you want, or
The real problem are the implicit type conversions in C++, which are so dangerous.
Convenient but can cause serious problems.
In that context I'd like to suggest to add an explicit statement to the construcutor
of matrices in ublas:
in matrix.hpp changing
matrix (const matrix_expression<AE> &ae):
to
explicit matrix (const matrix_expression<AE> &ae):
It gave me some surprise recently in my code, as it involves unnecessary copying of submatrices
I wasn't aware of.
Best regards,
Peter
-- -------------------------------------------------------------------------------------------- Dr. Peter Schmitteckert Center for Functional Nanostructures Institut für Theorie der Kondensierten Materie Karlsruhe Institute of Technology Universität Karlsruhe Wolfgang-Gaede Str. 1 D-76128 Karlsruhe