From: Matthew Kerwin <matthew@...>
Date: 2013-03-07T17:30:05+09:00
Subject: Re: Random#rand_inclusive?

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OTOH, without looking up exactly what Epsilon is (the smallest possible
absolute interval represented by a float?), wouldn't your technique fail if
max is big, because {big float} + {small float} = {big float} ?  I'd
suggest something clever with Rationals, personally, along the lines of
`(max*rand(range+1))/range"

Sent from my phone, so excuse the typos.
On Mar 7, 2013 5:56 PM, "Robert Feldt" <robert.feldt@gmail.com> wrote:

> Hi,
>
> Random#rand and Kernel#rand are exclusive i.e. they return a value >= 0.0
> but <max if max is a Float. What if one wants a rand that is inclusive of
> the max? Would any of the below approaches guarantee to give an inclusive
> range?
>
> class Random
>   # Return a random number between 0 (inclusive) and max (inclusive).
>   def rand_incl(max = 1.0)
>     if Float === max
>       rand(max+Float::EPSILON)
>     elsif Integer === max
>       rand(max+1)
>     end
>   end
>
>   # Same but with other strategy
>   def rand_incl2(max = 1.0)
>     if Float === max
>       num_floats = (max - min)/Float::EPSILON
>       min + rand(1+num_floats.to_i) * Float::EPSILON
>     elsif Integer === max
>       min + rand(max+1-min)
>     end
>   end
> end
>
> Thanks in advance,
>
> Robert Feldt
>
>

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<p>OTOH, without looking up exactly what Epsilon is (the smallest possible =
absolute interval represented by a float?), wouldn&#39;t your technique fai=
l if max is big, because {big float} + {small float} =3D {big float} ?=A0 I=
&#39;d suggest something clever with Rationals, personally, along the lines=
 of `(max*rand(range+1))/range&quot;</p>

<p>Sent from my phone, so excuse the typos.</p>
<div class=3D"gmail_quote">On Mar 7, 2013 5:56 PM, &quot;Robert Feldt&quot;=
 &lt;<a href=3D"mailto:robert.feldt@gmail.com">robert.feldt@gmail.com</a>&g=
t; wrote:<br type=3D"attribution"><blockquote class=3D"gmail_quote" style=
=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi,<div><br></div><div>Random#rand and Kernel#rand are exclusive i.e. they =
return a value &gt;=3D 0.0 but &lt;max if max is a Float. What if one wants=
 a rand that is inclusive of the max? Would any of the below approaches gua=
rantee to give an inclusive range?</div>

<div><br></div><div><div>class Random</div><div>=A0 # Return a random numbe=
r between 0 (inclusive) and max (inclusive).</div><div>=A0 def rand_incl(ma=
x =3D 1.0)</div><div>=A0 =A0 if Float =3D=3D=3D max</div><div>=A0 =A0 =A0 r=
and(max+Float::EPSILON)</div>

<div>=A0 =A0 elsif Integer =3D=3D=3D max</div><div>=A0 =A0 =A0 rand(max+1)<=
/div><div>=A0 =A0 end</div><div>=A0 end</div><div><br></div><div>=A0 # Same=
 but with other strategy</div><div>=A0 def rand_incl2(max =3D 1.0)</div><di=
v>=A0 =A0 if Float =3D=3D=3D max</div>

<div>=A0 =A0 =A0 num_floats =3D (max - min)/Float::EPSILON</div><div>=A0 =
=A0 =A0 min + rand(1+num_floats.to_i) * Float::EPSILON</div><div>=A0 =A0 el=
sif Integer =3D=3D=3D max</div><div>=A0 =A0 =A0 min + rand(max+1-min)</div>=
<div>=A0 =A0 end</div><div>=A0 end</div>

<div>end</div><div><br></div><div>Thanks in advance,</div><div><br></div><d=
iv>Robert Feldt</div><div><br></div></div>
</blockquote></div>

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