       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 == 1}, y[z], z][[1, 1, 2]]
> Evaluate[DSolve[{y'[z] == z, y == 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 == 1}, y[z], z][[1, 1, 2]],  {z, 0, 1}]
> Plot[Evaluate[DSolve[{y'[z] == z, y == 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 == 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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