       Re: substitution rules and patterns

• To: mathgroup at smc.vnet.net
• Subject: [mg3428] Re: [mg3410] substitution rules and patterns
• From: Allan Hayes <hay at haystack.demon.co.uk>
• Date: Wed, 6 Mar 1996 01:47:51 -0500
• Sender: owner-wri-mathgroup at wolfram.com

```Susan Rempe <rempe at euclid.chem.washington.edu>
[mg3410] substitution rules and patterns
>Could someone tell me why the first substitution rule
>works and the second doesn't----
>
>In:= (c^2)^(d/2)/.{(a_^2)^(b_ /2)->a^b}
>Out= c^d
>
>In:= (c^2)^(5/2)/.{(a_^2)^(b_ /2)->a^b}
>Out= (c^2)^(5/2)

Susan:

Mathematica sees the full forms:

(*1*) (c^2)^(d/2)//FullForm
Power[Power[c, 2], Times[Rational[1, 2], d]]

(*2*) (c^2)^(5/2)//FullForm
Power[Power[c, 2], Rational[5, 2]]

The left side of your rule (a_^2)^(b_ /2)->a^b has FullForm

(a_^2)^(b_ /2)//FullForm
Power[Power[Pattern[a, Blank[]], 2],
Times[Rational[1, 2], Pattern[b, Blank[]]]]

which matches (*1*) but not (*2*)

Allan Hayes
hay at haystack.demon.co.uk

==== [MESSAGE SEPARATOR] ====

```

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