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Re: Can someone explain why Mathematica is doing this?
*To*: mathgroup at smc.vnet.net
*Subject*: [mg19140] Re: [mg19113] Can someone explain why Mathematica is doing this?
*From*: "David Park" <djmp at earthlink.net>
*Date*: Thu, 5 Aug 1999 23:58:43 -0400
*Sender*: owner-wri-mathgroup at wolfram.com
Benjamin,
Mathematica does automatically make the simplification, undoing the substitution.
You could wrap Sin[x] and Cos[x] in HoldForm which would prevent the simplification,
then use ReleaseHold when you want to fully evaluate. Or you could use sin[x]/cos[x]
and then substitute the real names when you want to fully evaluate.
David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/
>I'm running Mathematica v3.0.1.1x (or something like that) on a Macintosh. I want
>to replace Tan[something] with Sin[something]/Cos[something]. The obvious
>substitution (see below) didn't work. Other substitutions work fine, but
>this one just sits there. Perhaps (it has just occured to me) Mathematica is
>making the substitution, but then "simplifying" Sin/Cos->Tan. However, I
>want to make other substitutions (to check some algebra that I'm doing by
>hand). How can I make Mathematica do this?
>
>Thanks in advnace,
>-Ben
>
>
>In[6]:=Tan[x]/.Tan[z_]->Sin[z]
>
>Out[6]=Sin[x]
>
>In[7]:=Tan[x]/.Tan[z_]->z Sin[z]
>
>Out[7]=x Sin[x]
>
>In[8]:=Tan[x]/.Tan[z_]->Sin[z]Cos[z]
>
>Out[8]=Cos[x] Sin[x]
>
>In[9]:=Tan[x]/.Tan[z_]->Sin[z]/Cos[z]
>
>Out[9]=Tan[x]
>
>--
>-------------------------------------------------------------------
> Benjamin Lotto *
> Department of Mathematics * e-mail: belotto at vassar.edu
> Vassar College, Box 349 * phone: 914-437-7180
> 124 Raymond Avenue * fax: 914-437-7065
> Poughkeepsie, NY 12604-0349 *
>-------------------------------------------------------------------
> WWW: <http://math.vassar.edu/faculty/lotto/lotto.html>
>-------------------------------------------------------------------
>
>
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