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From: John Maddock (john_at_[hidden])
Date: 2006-10-06 05:04:56

Janek Kozicki wrote:
> John Maddock said: (by the date of Wed, 4 Oct 2006 18:43:00 +0100)
>> Mathematical Special Functions
> how about sigmoid, double sigmoid and their derivatives? Used for
> neural networks.

Those are new ones to me.

> Just a suggestion. They are so simple, that perhaps you can assume
> that the user can write them himself (as it was done in the past).
> Unless you know some optimized way to implement them....

I suspect you will never improve on a call to exp() ?

Of course if you want 1 - sigmoid(x) then you can rearrange things to avoid
cancellation error. But I don't know how important such things are.

One of the problems we have is that there are a virtually unlimited number
of special functions, not least all those in TR1. So it's a case of trying
to draw the line in the right place, but do feel free to lobby for your
favorites :-)


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