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> >------------------------------------------------------------------- > >