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Newbie question about rules

• To: mathgroup at smc.vnet.net
• Subject: [mg21363] Newbie question about rules
• From: dougn_NOspam at gte.net (Doug Nelson)
• Date: Wed, 29 Dec 1999 14:15:49 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

Hello All,

I just received my copy of Mathematica 4.0 and I've been reading Mastering 
Mathematica.  

I'm trying to apply a rule that changes "Sin" to "Cos" in an expression.  It 
seems to work fine with normal expressions, but not with a Plot function. 

This works:
   exp2 := Abcfunc[Sin[x]]
   exp2 /. Sin -> Cos
out = Abcfunc[Cos[x]]

However, the following gives me a sine wave plot in both cases:

   exp := Plot[Sin[x], {x,0,2 Pi}]
   exp
out = < a sine wave plot >

   exp /. Sin -> Cos
out = < another sine wave plot ! >

Why don't I get a cosine plot?

Thanks in advance,
Doug

• Follow-Ups:
  • Re: Newbie question about rules
    • From: Ken Levasseur <Kenneth_Levasseur@uml.edu>