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Why D[x', x] isn't 0 ?

• To: mathgroup at smc.vnet.net
• Subject: [mg66094] Why D[x', x] isn't 0 ?
• From: "Vladimir" <vladimir347 at yahoo.com>
• Date: Sat, 29 Apr 2006 03:40:49 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

Hello!

D[x'', x']  =>  0  (* okay *)

D[x', x]  =>  x''  (* unexpected despite being similar to above *)

D[f[x'], x]  =>  x'' f'[x']  (* unexpected as well *)

Why the last 2 lines don't produce zeroes and how to make them
do so (for any function f) because it's quite common in mechanics
where velocity is treated as independent of position, etc.

--
Vladimir

• Follow-Ups:
  • Re: Why D[x', x] isn't 0 ?
    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>