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Re: Division by zero, despite strong hint

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96594] Re: [mg96542] Division by zero, despite strong hint
  • From: "David Park" <djmpark at comcast.net>
  • Date: Mon, 16 Feb 2009 16:42:15 -0500 (EST)
  • References: <7722908.1234786522774.JavaMail.root@m02>

You left out a comma.

g3[x_] := Piecewise[{{Sin[1/x], x != 0} , {0, x == 0}}]
Plot[g3[x], {x, -.1, .1}]

Help indicates that the routine evaluates the conditions first, without
evaluating the expressions, and picks the first condition that is true.
Also, it is possible in Plot that the value 0 was never used.


David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/  



From: dch888 [mailto:dch888 at googlemail.com] 

Hi,

I'm trying to plot the Sin[1/x] curve with the curve being defined as
0 at 0 like this:

g3[x_] := Piecewise[{{Sin[1/x], x != 0} {0, x == 0}}]

Invoking Plot produced a flat graph; puzzled I asked for g3[0] and
got:

Power::infy Infinite expression 1/0 encountered >>

{
 {Indeterminate, False True},
 {0, \!\(\*
    TagBox["True",
     "PiecewiseDefault",
     AutoDelete->False,
     DeletionWarning->True]\)}
}

Hmmm...  what's the trick here to stop Mathematica evaluating all the
branches
of the piecewise fn? There's nothing in the documentation that I can
see to stop this in Piecewise... perhaps I need to use a different
Mathematica 
function?

Thanks,
David.




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