Re: questions on ublas ?

From: jhrwalter (walter_at_[hidden])
Date: 2001-12-07 02:40:29

--- In boost_at_y..., Peter Schmitteckert (boost) <boost_at_s...> wrote:
> Salut,
> 
> On Thursday 06 December 2001 10:45, Toon Knapen wrote:
> 
> > >>For instance if I
> > >>need a temporary matrix in a loop, but in every loop the total 
size
> > >>of the matrix can be different, I can allocate a matrix with 
some
> > >>maximal size and resize it in every loop to something smaller 
in every
> > >>loop in constant amortised time ?
> > >
> > > Currently not, but it should be possible to change this. May be 
we
> > > need to differentiate size() and capacity()?
> >
> > Definitly. This would minimise memory allocation !
> 
> I also need this feature to avoid unneccessary allocation,
> but here should be the possiblilty to finally release unneeded 
memory.
> 
> What about the following idea:
> -> resize( n1, n2)  garanties "to hold size1 rows of size2 
elements".
> -> reserve(n3, n4) garanties that as long n3>=n1, n4 >=n2 no 
allocations in 
> resize(n1,n2) are performed. if n3<n1 or n4 < n2 the matrix is 
allowed to
> shrink to the reserved size if requested in a subsequent resize(..) 
in
> order to minimize wasted memory.
> But this would lead to the notion of a minimal_capacity().

Do we really need reserve()? IMO the allocation behaviour of resize() 
is a quality of implementation issue, especially since resize() is a 
method of the proxy concept. If we intend to make it's behaviour 
transparent, we'd have to introduce capacity() first. OTOH capacity() 
won't be generic.

BTW, do we need to consider std::allocator?
 
[snip]
 
Regards
 
Joerg