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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] matrix::linspace
- From: Hauke Heibel <hauke.heibel@xxxxxxxxxxxxxx>
- Date: Tue, 26 Jan 2010 20:55:17 +0100
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On Tue, Jan 26, 2010 at 7:56 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
> Hm. "high = (size-1)*s" is true to machine precision which is good
> enough.
This depends on your application. If you want something like this to work
VectorXd x = VectorXd::LinSpaced(-1.0,1.0,10000);
std:acos(x(0));
std::acos(x(end));
it better be in range or you'll end up with NaN when x(0)<-1 or
x(end)>-1. But maybe that's too application specific.
> The only idea that I see is that every, say, 8 iterations, you
> recompute the product with a multiplication (thus you get something
> good to machine precision) and you forget about the 'accumulated'
> value.
This will seriously decrease performance. I am just reading a bit over here
http://docs.sun.com/source/806-3568/ncg_goldberg.html
and I might give the 'Kahan Summation Formula' a try. At least it does
not include additional 'if' clauses.
- Hauke