Re: using N function
- To: mathgroup at smc.vnet.net
- Subject: [mg76379] Re: using N function
- From: Peter Pein <petsie at dordos.net>
- Date: Sun, 20 May 2007 02:44:03 -0400 (EDT)
- References: <f2me6h$lu4$1@smc.vnet.net>
kkwweett schrieb:
> Good morning Mathematica users,
>
>
> Can anyone tell me, please, which of a),b) or c) is wrong :
>
> a)
> <MathematicaHelp>
> <quote>
>
> N[expr] is equivalent to N[expr, MachinePrecision].
>
> </quote>
> </MathematicaHelp>
>
> b)
> In[1]:=N[Exp[Sqrt[163 ]Pi] - 6403203]
> Out[1]=256.
>
>
> c)
> In[2]:=N[Exp[Sqrt[163 ]Pi] - 6403203,$MachinePrecision]
> Out[2]=743.9999999999993
>
> ?
>
> Thank you
>
Hi,
don't mix MachinePrecision and $MachinePrecision!
b) and c) are wrong:
In[1]:= $Version
Out[1]= "5.2 for Linux x86 (64 bit) (June 20, 2005)"
In[2]:= N[Exp[Sqrt[163]*Pi] - 6403203]
Out[2]= 2.62537 * 10^17
In[3]:= N[Exp[Sqrt[163]*Pi] - 6403203, $MachinePrecision]
Out[3]= 2.625374126343655 * 10^17
which seems to be accurate, because:
In[4]:= NumberForm[N[Exp[Sqrt[163]*Pi] - 6403203, 10^4], {20, 15}]
gives (visually) the same output as in Out[3].
Regards,
Peter