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MathGroup Archive 2001

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Re: Naming pieces of patterns

  • To: mathgroup at smc.vnet.net
  • Subject: [mg29841] Re: Naming pieces of patterns
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Fri, 13 Jul 2001 04:19:22 -0400 (EDT)
  • References: <9ijhj3$rhj$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Cyril,

Unevaluated[-(1/(2a))]/. HoldPattern[ 1/(2 a)]\[Rule]A

-A

Unevaluated[{(a+b),-(a+b)}]/.a+b\[Rule] e

{e, -e}

Unevaluated[{-Sqrt[a+b],1/Sqrt[a+b]}]/.HoldPattern[Sqrt[a+b]]\[Rule]e

{-e, 1/e}

Unevaluated[{I,2 I,-I}]/.HoldPattern[I]\[Rule]J

{J, 2*J, -J}

{I,2 I,-I}/.Complex[0,y_]->y J

{J, 2*J, -J}

--
Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

"Cyril Fischer" <fischerc at itam.cas.cz> wrote in message
news:9ijhj3$rhj$1 at smc.vnet.net...
> How can I as simply as possible use "substitutions"
> 1.
> -(I/(2 a)) /. I/(2 a) -> A
> does not work, while
> (I/(2 a)) /. I/(2 a) -> A
> works well
>
> 2.
> {(a + b), -(a + b)}/. a + b -> e
> gives
> {e, -a - b}
> instead of {e,-e}
>
> 3.
> {-Sqrt[a + b], 1/Sqrt[a + b]} /. Sqrt[a + b] -> e
> gives
> {-e,1/Sqrt[a + b]}
>
> 4.
> {I, 2 I, -I} /. I -> J
> gives
> {J, 2 \[ImaginaryI], -\[ImaginaryI]}
>
> I know _why_ these cases do not work, but I would like to know, if there
> is a possibilty to use a common pattern rule to substitute all
> occurences of an expression.
>
> Thank you,
> Cyril Fischer
>
>




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