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Date:         Fri, 10 Mar 2017 21:21:29 -0800
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From: Christopher Rowley <c.a.rowley@ICLOUD.COM>
Subject: Re: Two more (simple) functions for l3fp
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Status: R

sign may well be a useful function, but hardly much to do with fp.

chris

> On 10 Mar 2017, at 16:49, Bruno Le Floch <blflatex@gmail.com> wrote:
> 
> On 03/09/2017 05:42 PM, Andrew Parsloe wrote:
>> Two functions which I think could be beneficially added to l3fp without
>> straining its role as a kernel module (in the way that, say, the gamma
>> function would) are the signature function (sgn) and a unit step
>> function (Heaviside? -- the difficulty is what value to assign at 0).
>> Given the numerical values assigned to true and false in l3fp, it is
>> easy to mimic these with simple inequalities (e.g. (#1 > 0) - (#1 < 0)
>> for sgn) but perhaps the functions should be there in the first place?
>> 
>> I found myself wanting these when considering a table of fp values where
>> it made sense to blank cells containing negative values which "got in
>> the way". The code creating the table contained the option of blanking
>> zero-value cells, so I multiplied the tabulated formula by 1 - (#1 < 0).
>> 
>> Andrew
>> 
>> ---
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> 
> Will copied your message to https://github.com/latex3/latex3/issues/346
> and replied there that
> 
>> sign() or sgn() definitely makes sense to me, but I’m not sure about
>> step() / heaviside() / whatever. Can you give another example for the
>> use case there?
> 
> I'm adding sign().  I don't think heaviside is needed: (#1) > 0 ? (#1) :
> 0 seems to do what you want pretty nicely.
> 
> What do you think?
> 
> Concerning Gamma, the main reason I haven't implemented it yet is that
> it requires determining some magic constants that were only given to me
> for a lower precision than what I need (10 digits instead of 16).
> 
> Bruno