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Re: [glas] Vector Spaces vs. "Objects called vectors"

From: Kevin Wheatley (hxpro_at_[hidden])
Date: 2005-02-04 05:26:35

Ian McCulloch wrote:
> Clearly, in a lot of cases it doesn't make sense to resize the vector.
> eg, "x += y", x and y should be the same size. The only case where it
> would be sensible to consider resizing is for ordinary assignment. Here,
> I don't think it is even sensible to fix a policy, if only for
> interoperability reasons (how would you prevent a resize for std::vector?
> How would you allow resize for a fixed-size array?).

x += y, what if x has a sparse representation? (OK so I'm playing
advocate here)

I think what your meaning is that the size (math?) is like the
capacity (CS) and that x and y have the same notional
capacity/dimensionality. This would be a different thing to the
underliying storage capacity/size which may need to be modified.

Is this a desirable property of a vector (and thus by orthoganally a
matrix), to be able to allow the user of the objects to stop
themselves from incurring this 'hidden' memory allocation cost. I
think it is.

Conversly is it desirable to allow flexibility and the user to care
less about the underlying representation, also a yes I think.


a point of variation in policy is probably needed for storage
maybe dimensionality miss-match is an error - provide an explicit
conversion mechanism like a dimensionality_cast<>() ?
a glossary/dictionary of terms and concepts is important (most
important?) to progress anywhere between the two meeting groups


| Kevin Wheatley, Cinesite (Europe) Ltd | Nobody thinks this      |
| Senior Technology                     | My employer for certain |
| And Network Systems Architect         | Not even myself         |