       • To: mathgroup at smc.vnet.net
• Subject: [mg31894] Re: Simple questions about Mathematica
• From: atelesforos at hotmail.com (Orestis Vantzos)
• Date: Mon, 10 Dec 2001 06:14:34 -0500 (EST)
• References: <9uvhm2\$ibq\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```The answer to your first question is NOT an easy one! You see
"substitution rules" or "transformation rules" are at the very core of
what Mathematica is, so there are a lot of things to learn about them.
Anyway here is a basic example:
Sqrt[a^2+b^2]+Exp[Sqrt[a^2+b^2]]/.Sqrt[a^2+b^2]->R
will return R+Exp[R]
What does it all mean?
expr/.Sqrt[a^2+b^2]->R means take expr and substitute all occurences
of Sqrt[a^2+b^2] with R
specificaly the chapters concerning patterns and rules, and you will
find many interesting things that will get you started towards being a
full-fledged Mathematica programmer.
The answer to your second question IS simple: create a notebook with
your calculation and you can run it again whenever you want. If you
want to change something from one evaluation to another, define a
proper global variable and change that.
Orestis

```

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