Re: a bug in RealDigits? Mathematica 5.0
- To: mathgroup at smc.vnet.net
- Subject: [mg45220] Re: a bug in RealDigits? Mathematica 5.0
- From: drbob at bigfoot.com (Bobby R. Treat)
- Date: Sun, 21 Dec 2003 03:42:13 -0500 (EST)
- References: <bs1btt$9pt$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
The number of digits given in First@RealDigits@t is Floor@Precision@t,
so the problem is in the assumed precision of your input. Mathematica
assumes the last digit you enter is in doubt, and the number's
uncertainty dx can be computed as follows (hinted at in Help):
t= 39383738378094852309445543850343.49494;
Solve[-Log[10, dx/t]==Precision@t,dx]
{{dx->0.00001}}
You can enter it this way instead:
t= 39383738378094852309445543850343.49494`37;
c=First@RealDigits@t
Length@c
{3,9,3,8,3,7,3,8,3,7,8,0,9,4,8,5,2,3,0,9,4,4,5,5,4,3,8,5,0,3,4,3,4,9,4,9,4}
37
Bobby
nma124 at hotmail.com (steve_H) wrote in message news:<bs1btt$9pt$1 at smc.vnet.net>...
> hello;
>
> Mathematica 5.0, student version, on XP home edition:
>
> t1 = 39383738378094852309445543850343.49494
>
> {c, d} = RealDigits[t1];
>
> now c is
>
> {3, 9, 3, 8, 3, 7, 3, 8, 3, 7, 8, 0, 9, 4, 8, 5, 2, 3, 0, 9,
> 4, 4, 5, 5, 4, 3, 8, 5, 0, 3, 4, 3, 4, 9, 4, 9}
>
> notice that I typed in the last digits of t1 as '.49494', i.e the
> number to the right of the decimal point.
>
> But 'c' above is missing the last digit, it only reports '4,9,4,9'
> instead of '4,9,4,9,4'
>
> What happened to the last digit '4' ?