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(Newbie) Replace without Evaluation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg9610] (Newbie) Replace without Evaluation
  • From: Halldor Bjornsson <hbjorn at po-box.mcgill.ca>
  • Date: Fri, 14 Nov 1997 21:39:52 -0500
  • Organization: McGill University
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,
This is probably an elementary question:

I am manipulating differential equations, and am having trouble with
getting Mathematica to stop evaluating everything fully.

A trivial example of my problem is the following:

In[1]: = z[x_]=Exp[2 x];

In[2]:= dz=D[z[x],x]
Out[2]= 2 Exp[2x]

If I want to write this as  "dz=2 z[x]" and do

dz /. {Exp[2] -> z[x]}

I will still get  2 Exp[2x] out since z[x] is evaluated after the
replacement.  Delayed replacement  (" :>" does not seem to help.

Anyone know how to replace without evaluation ?
 

Thanks,

Halldor



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