Re: How to treat this false singular point?
- To: mathgroup at smc.vnet.net
- Subject: [mg68440] Re: How to treat this false singular point?
- From: "Ray Koopman" <koopman at sfu.ca>
- Date: Sat, 5 Aug 2006 03:46:40 -0400 (EDT)
- References: <easkcp$g3j$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
simon yang wrote:
> Dear everyone,
> I have a function:
> f[x_]:=(x-x1)Log[Abs[x-x1]] + (x-x2)Log[Abs[x-x2]] + ... +
> (x-xn)Log[Abs[x-xn]],
> {x1,x2,...,xn}={100,200,300,...} for instance
> How to get value: f[x] as there are different singular at different x?
> I know at x=xn, f[x]==1, But Mathematica return: "Indeterminate", What
> should I do?
> what others do in C++, Fortran ?
The easiest way would be
Unprotect[Log]; Log[0] = 0; Log[0.] = 0; Protect[Log];
That would do what you want here, but might cause problems elsewhere.
Another way would be to define a new function
xLog[0] = 0; xLog[0.] = 0; xLog[x_] := x*Log[Abs[x]]
Then
f[x_] := Tr@Map[xLog,x-{100,200,...}]