MathGroup Archive 2007

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Sort with -Infinity fails


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


  • Prev by Date: Re: Sort with -Infinity fails
  • Next by Date: RE: change filename automatically in Export Command
  • Previous by thread: Re: Sort with -Infinity fails
  • Next by thread: Re: Sort with -Infinity fails