Re: Overly complicated reductions?

*To*: mathgroup at smc.vnet.net*Subject*: [mg77626] Re: Overly complicated reductions?*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Thu, 14 Jun 2007 05:20:13 -0400 (EDT)*Organization*: The Open University, Milton Keynes, UK*References*: <f4om08$7bj$1@smc.vnet.net>

David Rees wrote: > Consider f(x)=e^(-2x) > > I wanted to retreive the inverse function f^-1(x), Mathematica to the > rescue: > \!\(Reduce[y == E\^\(\(-2\) x\), x]\) > > \!\(C[1] \[Element] Integers && y != 0 && > x == 1\/2\ \((2\ \[ImaginaryI]\ \[Pi]\ C[1] + Log[1\/y])\)\) > > This can't be right, I can rearrange it to just Ln(x)/-2 on paper. What did > I do wrong? > > Thanks You could specify a domain to get something closer to what you are looking for. For instance, In[1]:= Reduce[y == E^(-2*x), x, Reals] Out[1]= y > 0 && x == (1/2)*Log[1/y] Regards, Jean-Marc