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MathGroup Archive 1999

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Re: Can someone explain this?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19150] Re: Can someone explain this?
  • From: Bruno Daniel <bruno.daniel at hadiko.de>
  • Date: Thu, 5 Aug 1999 23:58:51 -0400
  • Organization: University of Karlsruhe
  • References: <7obcl4$3te@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Benjamin

Sin[x]/Cos[x] is simplified to Tan[x] whenever it occurs in an
expression. You can prevent this by wrapping it with HoldForm:

In[1]:=
x y Tan[x] + Tan[y]     /. Tan[z_]->HoldForm[Sin[z]/Cos[z]]

Out[1]= 
x y Sin[x] / Cos[x] + Sin[y] / Cos[y]

The expression Sin[x] / Cos[x] is then kept because it is in the
Hold status. You can release all holds in an expression with
ReleaseHold:

In[2]:= % // ReleaseHold
Out[2] = x y Tan[x] + Tan[y]

Yourse sincerely
  Bruno


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