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Subject: Re: [boost] RFC: runtime-flexible arrays
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2012-02-16 02:17:32

On 02/16/2012 02:42 AM, Bjoern Andres wrote:
> Hi everyone,
> I have written a header for runtime-flexible multi-dimensional views and
> arrays and would love to get comments and feedback from the boost
> community:
> tutorial code :
> main website :
> doxygen reference doc:
> git repository :
> tech report :
> Unlike in Boost.MultiArray, the dimension of arrays is not a template
> parameter in Marray.

In Boost.MultiArray, the dimension is not a template parameter; the
number of dimensions is.

I assume you always use the maximum number of dimensions, and treat
arrays of size N*M the same as arrays or size N*M*1*1*1*1

> Other features include
> - runtime-flexible dimension, shape, size and indexing order (first or
> last coordinate major order)

> - arithmetic operators with automatic type promotion and expression
> templates.

This should be decoupled from the container itself.
Algorithms and containers are different things.

If you're doing expression templates, you should re-use Boost.Proto to
have a proper framework to deal with expression trees.

And if you're supporting arithmetic operators, it will be expected that
you generate high-performance parallel code (like Blitz++, Eigen, or NT2
-- I am the author of the latter).

I'm not sure type promotion is such a good idea.

> - access to entries via coordinates, scalar indices and STL-compliant
> random access iterators.

I find it confusing that iterators flatten the data. I'd rather they
iterate on the external dimension.
If you want to iterate over flattened data just make a view with a
flattened shape and iterate that.

Also if you support 1D and nD access, why not also support 2D or 3D
access within a 4D array?

Something else, what we do in NT2 is that we use an iliffe index as
described in the NRC (Numerical Recipes for C) book. This allows us to
make a view that extracts an arbitrary rectangle or hypercube and to add
padding between lines without extra modulo operations.
Do you use something like that as well?

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