Re: Replacement question

• To: mathgroup at smc.vnet.net
• Subject: [mg74193] Re: Replacement question
• From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
• Date: Wed, 14 Mar 2007 03:44:35 -0500 (EST)
• Organization: The Open University, Milton Keynes, UK
• References: <et5nnh\$jhk\$1@smc.vnet.net>

Brian Beckage wrote:
> I apologize for this very basic question.  I understand how to use /.
> {} to replace a  variable with a more complex expression, e.g., x->
> y+z.  Can one move in the opposite direction to replace all
> occurrences of y+z with x?   myExpression/.{y+z->x} does not seem to
> work.

That works:

In[1]:=
expr = z + y + a + b + 2*c + 2*d;
expr /. y + z -> x

Out[2]=
a + b + 2 c + 2 d + x

Now, could you, please, post an example of an expression for which the
replacement rule does not work?

Regards,
Jean-Marc

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