Re: Reduce/Solve
- To: mathgroup at smc.vnet.net
- Subject: [mg49997] Re: Reduce/Solve
- From: ab_def at prontomail.com (Maxim)
- Date: Tue, 10 Aug 2004 06:02:54 -0400 (EDT)
- References: <cf7djh$3na$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
An even simpler example: In[1]:= Reduce[x == E^(a*x), x] Reduce[x == E^(y*x), x] Out[1]= Reduce[x == E^(a*x), x] Out[2]= C[1] \[Element] Integers && y != 0 && x == -(ProductLog[C[1], -y]/y) What's more, Out[2] is incorrect because it misses the x==1&&y==0 case. Maxim Rytin m.r at inbox.ru "Dana DeLouis" <delouis at bellsouth.net> wrote in message news:<cf7djh$3na$1 at smc.vnet.net>... > Hello. It is because of Mathematica's huge bug in variable names. Reduce > often doesn't work because of this bug. The first thing you need to try is > to change the variable name. I would first start by changing the "r" to a > variable name that comes near the beginning of the alphabet, like "a" (at > least something before the "d" in the equation). > > Taking your equation, and changing r to a: > > eq = J == J0*(1 + r/d)*Exp[-(r/d)] /. r -> a > > J == ((1 + a/d)*J0)/E^(a/d) > > Now it should work: > > tt = Reduce[eq, a] > > d != 0 && J == 0 && > (J0 == 0 || a == -d) || > C[1] ? Integers && > J != 0 && J0 != 0 && > d != 0 && a == > -d - d*ProductLog[C[1], > -(J/(E*J0))] > > HTH > Sad, isn't it! > > Dana > > > "Dr A.H. Harker" <a.harker at ucl.ac.uk> wrote in message > news:cetf3i$6i8$1 at smc.vnet.net... > > Dear All, > > I tend to think of Reduce as a more powerful tool than Solve, > > yet with > > > > eq = J == J0 (1 + r/d) Exp[-r/d] > > ss = Solve[eq, r] > > tt = Reduce[eq, r] > > > > I get useful output from Solve, but Reduce returns the expression > > unevaluated. What am I missing? Mathematica 5.0.0.0 under Windows XP. > > > > Tony > > > > Dr A.H. Harker > > Director of Postgraduate Studies > > Deputy Head, Condensed Matter and Materials Physics Group > > Department of Physics and Astronomy > > University College London > > Gower Street > > LONDON > > WC1E 6BT > > (44)(0)207 679 3404 > > a.harker at ucl.ac.uk > > > > > >