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MathGroup Archive 2002

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Re: Why these graphs differ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg33942] Re: Why these graphs differ?
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Wed, 24 Apr 2002 01:21:50 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <aa3gm6$80q$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de
  • Sender: owner-wri-mathgroup at wolfram.com

Vladimir Bondarenko wrote:
> 
> 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?

The Part[expr,1,1,2] is z for expr:> DSolve[{y'[z] == z, y[0] == 1},
y[z], z]

and the Part[expr,1,1,2] is (2+z^2)/2 for expr:>  {{y[z] -> (2 +
z^2)/2}}

so there is no wonder, that the results are differnt. Different
expressions
may have also different parts.

Regards
  Jens


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