Re: ReplaceAll / sequential replacements versus joint replacement

• To: mathgroup at smc.vnet.net
• Subject: [mg55452] Re: [mg55429] ReplaceAll / sequential replacements versus joint replacement
• From: "Wolf, Hartmut" <Hartmut.Wolf at t-systems.com>
• Date: Thu, 24 Mar 2005 03:41:51 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```

>-----Original Message-----
>From: Ronald Wendner [mailto:Ronald.Wendner at uni-graz.at]
To: mathgroup at smc.vnet.net
>Sent: Wednesday, March 23, 2005 11:35 AM
>Subject: [mg55452] [mg55429] ReplaceAll / sequential replacements versus
>joint replacement
>
>Suppose there is an expression e1 which depends, among others,
>on variables
>a and b.
>Replace both a and b by zero:
>
>e1/.{a->0,b->0} Mathematica gives, say, result1.
>
>Next, consider
>
>e2 = e1/.{a->0};
>e2/.{b->0} Mathematica gives, say, result2.
>
>How can result 1 differ from result 2?
>
>For my specific problem, I also attach a short Mathematica notebook.
>[Contact the author to obtain the notebook - moderator]
>
>I'd appreciate any help.
>
>Many thanks,
>Ron
>
>
>

Ron,

see Help:

"ReplaceAll looks at each part of expr, tries all the rules on it, and
then goes on to the next part of expr. The first rule that applies to a
particular part is used; no further rules are tried on that part, or on
any of its subparts."

This makes it clear: there *are* differences.  For your special problem,
publish it (according to the rules of this group).

--
Hartmut Wolf

```

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