Re: Transformations in expressions

• To: mathgroup at smc.vnet.net
• Subject: [mg91891] Re: Transformations in expressions
• From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
• Date: Fri, 12 Sep 2008 05:25:47 -0400 (EDT)
• Organization: The Open University, Milton Keynes, UK
• References: <gaar3o\$16q\$1@smc.vnet.net>

```Miguel wrote:

> How can I to transform a specific expression to other by substitution
> of a part of it.
>
> For example, I want to transform the expression Log[x^2+y^3]/
> Sin[x^2+y^3] in Log[z]/Sin[z] by substitution x^2+y^3 --> z.

You could write a transformation rule ("->") and apply it thanks to the
replacement operator ("/.")

In[1]:= expr = Log[x^2 + y^3]/Sin[x^2 + y^3] ;
expr /. x^2 + y^3 -> z

Out[2]= Csc[z] Log[z]

> And other question: Is the new expression dependent of z. I see it is,
> but how can I to programar it.

In[3]:= f[z_] = Log[x^2 + y^3]/Sin[x^2 + y^3] /. x^2 + y^3 -> z
f[2]
% // N

Out[3]= Csc[z] Log[z]

Out[4]= Csc[2] Log[2]

Out[5]= 0.762289

You should have a look at

tutorial/DefiningFunctions

http://reference.wolfram.com/mathematica/tutorial/DefiningFunctions.html

Regards,
-- Jean-Marc

```

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