Re: 1 equals 3 (among others)
- To: mathgroup at smc.vnet.net
- Subject: [mg32188] Re: 1 equals 3 (among others)
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Sat, 5 Jan 2002 00:10:24 -0500 (EST)
- Organization: Universitaet Leipzig
- References: <a13v7l$dgb$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
> Can anyone explain to me what is going on here? Look at this:
>
> In[1]:=f[x_] = (4 - x + Sqrt[-4*(3 - x) + (x - 4)^2])/2;
> In[2]:=Simplify[-4*(3 - x) + (x - 4)^2]
> Out[2]=(-2 + x)^2
>
> Well, right now we can be pretty sure that f[x]=1 for all x.
huuuu, since when is
(4 + Abs[x - 2] - x)/2
always 1 ? for all x
A new finding at the TU Berlin ?
Sqrt[a^2] is Abs[a] and *not* a !
> But
> Mathematica (4.0.2.0X) seems to know better:
>
> In[3]:=Map[f[#1]&, {0, 0.1, 1.7, 2, 2.5, 3}]
> Out[3]={3, 2.9, 1.3, 1, 1., 1}
it knows it better.
>
> It took me hours to find this error in my rather complex setting...;-(
hopfully is was your last error.
But you don't report *all* of *your* errors to
the mathgroup.
Regards
Jens