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MathGroup Archive 2002

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Re: Why these graphs differ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg33966] Re: [mg33925] Why these graphs differ?
  • From: BobHanlon at aol.com
  • Date: Wed, 24 Apr 2002 01:23:05 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

In a message dated 4/23/02 8:04:47 AM, vvb at mail.strace.net writes:

>These solutions, naturally, coincide.
>
>         DSolve[{y'[z] == z, y[0] == 1}, y[z], z][[1, 1, 2]]
>Evaluate[DSolve[{y'[z] == z, y[0] == 1}, y[z], z][[1, 1, 2]]]
>
>(2 + z^2)/2
>(2 + z^2)/2
>
>
>But, surprisingly, the corresponding graphs are not identical:
>
>Plot[         DSolve[{y'[z] == z, y[0] == 1}, y[z], z][[1, 1, 2]],  {z,
>0, 1}]
>Plot[Evaluate[DSolve[{y'[z] == z, y[0] == 1}, y[z], z][[1, 1, 2]]], {z,
>0, 1}]
>
>
>Is it a feature or a problem?


"Plot evaluates its arguments in a non-standard way (see Section A.4.2). You 
should use Evaluate to evaluate the function to be plotted if this can safely 
be done before specific numerical values are supplied. "


Bob Hanlon
Chantilly, VA  USA


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