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MathGroup Archive 1999

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Problem with conditional definitions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19464] Problem with conditional definitions
  • From: "Kevin J. McCann" <kevin.mccann at jhuapl.edu>
  • Date: Sat, 28 Aug 1999 15:52:59 -0400
  • Organization: Johns Hopkins University Applied Physics Lab, Laurel, MD, USA
  • Sender: owner-wri-mathgroup at wolfram.com

I have recently uncovered a problem with conditional definitions of
functions.  The following is a simple example

Remove[f]

f[x_ /; x <= 0] := x^2
f[x_ /; 0 < x < 1] := x^3
f[x_ /; x >= 1] := x^4

{f[1.], f'[1.],f''[1.]}

{1.,3.54208,18.8746}

Clearly incorrect. Or

{f[1.1],f'[1.1],f''[1.1]}

             {1.4641, 5.28974, 8.77428}
Correct: {1.4641, 5.324,  14.52}

So it is not that the function was evaluated at a boundary.

Also, if I use exact arguments:

{f[1],f'[1],f''[1]}

{1,f'[1],f''[1]}

None of the function definitions lead to the answers I got. Did I miss
something?
--

Kevin J. McCann
Johns Hopkins University APL





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