Re: Sort with -Infinity fails
- To: mathgroup at smc.vnet.net
- Subject: [mg73892] Re: Sort with -Infinity fails
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Fri, 2 Mar 2007 06:48:18 -0500 (EST)
- Organization: The Open University, Milton Keynes, UK
- References: <es6d0l$rmr$1@smc.vnet.net>
Tom Aldenberg wrote:
> Dear MathGroup,
>
> Minus Infinity (-Infinity) is smaller than -8, but Sort does not sort it as
> expected.
> Is there a Real minus Infinity?
>
>
> In[75]:=
> -Infinity < -8
> Out[75]=
> True
>
> In[76]:=
> Sort[{-Infinity, -8, 5}]
> Out[76]=
> {-8, 5, -â??}
Negative infinity is not a number but an expression:
In[1]:=
Head /@ {-Infinity, -8, 5}
Out[1]=
{DirectedInfinity,Integer,Integer}
In[2]:=
FullForm[-Infinity]
Out[2]//FullForm=
DirectedInfinity[-1]
Try your own ordering function to force the numerical evaluation as a
real. For instance,
In[3]:=
Sort[{-Infinity, -8, 5}, #1 < #2 & ]
Out[3]=
{-Infinity, -8, 5}
Regards,
Jean-Marc