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MathGroup Archive 2006

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

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


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.


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