Re: algebraic substitution rules
- To: mathgroup at smc.vnet.net
- Subject: [mg30736] Re: algebraic substitution rules
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Sun, 9 Sep 2001 03:26:25 -0400 (EDT)
- Organization: Universitaet Leipzig
- References: <9ncfq6$pt5$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
the onlyne help say:
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
since a_ match to the full expression the rule a_->Expand[a]
is used and no future rules are tried on that part.
You mean
1 + x^2 + x^3 + x^4 /.
{x^2 -> 1 + y, x^3 -> y(1 + y), x^4 -> (1 + y)^2} /.
a_ :> Expand[a]
Regards
Jens
Cattiaux Isabelle wrote:
>
>
> Hi,
>
> Could someone tell me why the first substitution rule
> works and the second doesn't
>
> In[1]:==
> 1+x^2+x^3+x^4 /. {x^2->1+x ,x^3->x(1+x) ,x^4->(1+x)^2}
>
> Out[1]==
> 2 + x + x(1 + x)+ (1 + x)^2
>
> In[78]:==
> 1+x^2+x^3+x^4 /. {x^2->1+x ,x^3->x(1+x) ,x^4->(1+x)^2,a_->Expand[a]}
>
> Out[78]==
> 1 + x^2 + x^3 + x^4
>
> --
> Isabelle Cattiaux-Huillard
> Universite de Valenciennes