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