Re: Student Problem
- To: mathgroup at smc.vnet.net
- Subject: [mg63819] Re: [mg63768] Student Problem
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Sun, 15 Jan 2006 05:43:31 -0500 (EST)
- References: <200601140732.CAA00252@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
On 14 Jan 2006, at 08:32, Dr A.H. Harker wrote:
> Dear All,
>
> I've often thought that one of the sneakiest things that
> Mathematica does to a beginner is the way it punishes him or her for
> mistyping the boundary conditions for DSolve, for example {...y'[0]
> =1,...}.
> One can come up with reasonable explanations for the fact that this
> mistaken
> assignment is associated with Derivative rather than y, and one
> used to be
> able to demonstrate this by typing ??Derivative before mopping up
> the mess
> with Clear[Derivative]. In Mathematica 5.1 ??Derivative does not show
> the associated y'[0]=1, making the use of Clear[Derivative] look like
> a strange folk remedy to the beginner. Any comments?
>
> Tony Harker
> Department of Physics and Astronomy
> University College London
> Gower Street
> LONDON
> WC1E 6BT
> (44)(0)207 679 3404
> a.harker at ucl.ac.uk
>
>
>
You are right and this looks to me like some sort of bug.
Nevertheless you can still do:
Derivative[1][y][0] = 1;
First[SubValues[Derivative]]
HoldPattern[Derivative[1][y][0]] :> 1
which also makes it fairly clear what has happened.
Andrzej Kozlowski
- References:
- Student Problem
- From: "Dr A.H. Harker" <a.harker@ucl.ac.uk>
- Student Problem