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MathGroup Archive 2006

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Re: How to treat this false singular point?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg68408] Re: [mg68406] How to treat this false singular point?
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Fri, 4 Aug 2006 03:59:21 -0400 (EDT)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

f[x_, xList_List] := Total[(x-xList)*Log[Abs[x-xList]]];

f[x, {x1, x2, x3}]

(x - x1)*Log[Abs[x - x1]] + (x - x2)*Log[Abs[x - x2]] + (x - x3)*Log[Abs[x - x3]]

a singularity will exist for each value of x in xList; therefor, f[xn, xList] cannot have the value 1

f[5. - 10^-15, Range[5]]

10.2273

Plot[f[x,Range[5]],{x,-1,5}];


Bob Hanlon

---- simon yang <yanshanguke at 163.com> 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 ?
> 


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