Re: Table through zero...strange
- To: mathgroup at smc.vnet.net
- Subject: [mg67033] Re: Table through zero...strange
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Wed, 7 Jun 2006 05:10:19 -0400 (EDT)
- Organization: The Open University, Milton Keynes, UK
- References: <e63mqt$kqd$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
leptonic wrote:
> Hello,
>
> When i type in Mathematica (version 4) Table[x, {x, -0.1, 0, 0.02}]
>
> it gives me {-0.1, -0.08, -0.06, -0.04, -0.02, -3.46945 x 10-18]}
> but for example Table[x, {x, -0.1, 0, 0.05}] will give a reasonable
> {-0.1, -0.05, 0.}.
This is due to the arithmetic used for the computation:
machine-precision in this case. The last entry is so close to zero that
it can be deemed as equivalent to zero; use the built-in function Chop
[1] to get the desired result {see In[1] and In[2]) or you may also use
exact arithmetic by typing exact numbers as in inputs In[3] and In[4].
In[1]:=
Table[Chop@x, {x, -0.1, 0, 0.02}]
Out[1]=
{-0.1, -0.08, -0.06, -0.04, -0.02, 0}
In[2]:=
Chop@Table[x, {x, -0.1, 0, 0.02}]
Out[2]=
{-0.1, -0.08, -0.06, -0.04, -0.02, 0}
In[3]:=
Table[x, {x, -1/10, 0, 2/100}]
Out[3]=
1 2 3 1 1
{-(--), -(--), -(--), -(--), -(--), 0}
10 25 50 25 50
In[4]:=
N@Table[x, {x, -1/10, 0, 2/100}]
Out[4]=
{-0.1, -0.08, -0.06, -0.04, -0.02, 0.}
HTH,
Jean-Marc
[1]: http://documents.wolfram.com/mathematica/functions/Chop