Re: [ublas] compressed_vector::resize() is not fully implemented (does not preserve data)

From: Gunter Winkler (guwi17_at_[hidden])
Date: 2006-06-29 04:29:03

On Wednesday 28 June 2006 19:46, Vassilis Virvilis wrote:

> By looking at sparse_vector.hpp one can see the compressed_vector::resize()
> is not implemented for the preserving case. How difficult is this to be
> implemented? Looks easy enough but then why it hasn't been implemented so
> far?

Because preserving data usually makes no sense in numerical applications. This 
flag has been introduced long time ago, but we decided to not fully support 
preserving resize in all classes. It can be much better implemented as a free 
function that knows which and how to transfer the data from old to new 
storage. If you just want a container which can grow and shrink arbitrarily 
std::vector is much more efficient.

BTW, for sparse vectors it is easy to decide which elements can be preserved. 
But for dense matrix you have different choices: throw away some 
rows/columns, create zero filled new columns, reorder matrix entries 
(=reshape) ...

mfg
Gunter

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