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
Asks
>Could someone tell me why the first substitution rule
>works and the second doesn't----
>
>In[70]:= (c^2)^(d/2)/.{(a_^2)^(b_ /2)->a^b}
>Out[70]= c^d
>
>In[71]:= (c^2)^(5/2)/.{(a_^2)^(b_ /2)->a^b}
>Out[71]= (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
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