Re: Sort
- To: mathgroup at smc.vnet.net
- Subject: [mg19176] Re: [mg19152] Sort
- From: "Wolf, Hartmut" <hwolf at debis.com>
- Date: Tue, 10 Aug 1999 02:52:40 -0400
- Organization: debis Systemhaus
- References: <199908060358.XAA08207@smc.vnet.net.>
- Sender: owner-wri-mathgroup at wolfram.com
Hermann Meier schrieb:
>
> Sort is not reliable. Try the following (Mathematica Version 4):
>
> In[1]:=
> Sort[{0, -Sqrt[2], 5}]
>
> Out[1]=
> {0, 5, -Sqrt[2]}
>
> In[2]:=
> Sort[{0., -Sqrt[2], 5}]
>
> Out[2]=
> {0., 5, -Sqrt[2]}
>
> One has to apply N to the list to get the correct result:
>
> In[3]:=
> Sort[N[{0., -Sqrt[2], 5}]]
>
> Out[3]=
> {-1.414213562, 0., 5.}
>
> HM
Hermann, of course Sort is reliable, but without applying N it doesn't
know anything of the value of Sqrt[2]. But you can make Sort to know
that if you just do
In[1]:= exactnumbers = {0, -Sqrt[2], 5};
In[4]:= Last /@ Sort[Transpose[{N[exactnumbers], exactnumbers}]]
Out[4]= {-Sqrt[2], 0, 5}
Sometimes perhaps, you have to be cautious with the numerical precision
you are using.
kind regards, hw
- References:
- Sort
- From: "Hermann Meier" <hmeier@webshuttle.ch>
- Sort