[GiNaC-list] table and exhashmap

[Sheplyakov Alexei]

On Mon, Feb 19, 2007 at 03:45:03PM +0800, Jerome BENOIT wrote:

> Let be more specific.
> 
> During some kind of computation I have to compute (multi-indexed) 
> coefficients:
> 1] these coefficients are long to compute;
> 2] they are computed by sub set through (consuming) recurrence formulae;
> 3] these coefficients are meant to be used randomly and very often.

> Clearly the remember machinery can be use to overcome point [1] and [3]:
> for GiNaC function this is transparent for the user.
> 
> Point [2] causes me some difficulty:
> I want to compute each subset only once.

> Hence the idea to compute each subset through a GiNaC function
> (with the remember option) which return tables,

Why do you need _GiNaC_ function to compute coefficients? What's wrong
with C++ function, e.g.

ex compute(const ex& data)
{
  static exmap remember;
	exmap::iterator i = remember.find(data);
	if (i != remember.end())
		return i->second;

	ex result;
	// actually compute it, making use of compute() itself
	
	remember.insert(exmap::value_type(data, result));
	return result;
}

> Right now, my guess is that I have to introduce a super class
> with a exhashmap<SOMETHING> as (principal) member: I thought
> that there was a better GiNaC way to do so, but apparently not.

Unless I'm missing something fundamental, this approach seems to be
unnecessary complicated.


Best regards,
 Alexei

-- 
All science is either physics or stamp collecting.

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