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>
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