Re: Question on subst(), deferred evaluation and trap()

[Jack Brennen <jfb@brennen.net>]

On 2/15/2012 12:25 PM, Bill Allombert wrote:
> > So far, the best I've come up with is:
> >
> >    V=[1/(x-1),1/(x-2),1/(x-3)];
> >
> > And then instead of a simple subst() on V, I use:
> >
> >    N=3;vector(#V,j,trap(,0,subst(V[j],x,N)))
> >
> > However, for cases where the trap is not taken, my method is about
> > 10 times slower than just doing subst(V,x,N).
>
> So your problem boils down to performance.
> What is your OS and PARI/GP version ?
>
> I ask because it seems trap is much slower on your system than on our test systems.

Yeah, it's just a performance issue.  My solution works, but
10x slowdown is hard to take.

That particular timing number was from 2.3.5-release, on FreeBSD
8.2-RELEASE, Intel i3-550 @ 3.2 GHz.


Karim's response about a potential solution in 2.5 may prompt me
to update to the latest PARI.