RE: 4.1 wont Solve LogNormal that 3.x could?

*To*: mathgroup at smc.vnet.net*Subject*: [mg35959] RE: [mg35923] 4.1 wont Solve LogNormal that 3.x could?*From*: "DrBob" <majort at cox-internet.com>*Date*: Fri, 9 Aug 2002 05:18:07 -0400 (EDT)*Reply-to*: <drbob at bigfoot.com>*Sender*: owner-wri-mathgroup at wolfram.com

No... my use of Simplify had nothing to do with it; I just wanted to see simple answers. My solution does things in a certain order and avoids the step that Solve had trouble with. The fact that Mathematica doesn't Simplify Log[Exp[x]] is just an example of what might seem correct but isn't quite right; it's not necessarily the specific problem in your situation. Bobby -----Original Message----- From: Nicholas Georgakopoulos [mailto:georgakopoulos at mindspring.com] To: mathgroup at smc.vnet.net Subject: [mg35959] Re: [mg35923] 4.1 wont Solve LogNormal that 3.x could? Your code works even if all Simplify[ ] are removed. Doesn't that negate the proposition that M'ca 4.1 refuses to solve due to proper refusal to simplify? ----- Original Message ----- From: "DrBob" <majort at cox-internet.com> To: mathgroup at smc.vnet.net Subject: [mg35959] RE: [mg35923] 4.1 wont Solve LogNormal that 3.x could? > I don't know why 4.2 considered it unsolvable, but it could be because > 4.2 knows more, not less. 4.2 is unwilling to simplify Log[E^x] to x, > for instance, probably because of concerns about the many possible > branches of Log. In the error message a bad equation is listed that > essentially equates two logarithms. You or I would simplify by > exponentiating each, but 4.2 knows that branch issues make that not > quite right. > > Anyway, here's a solution in 4.2 that avoids the problem: > > Off[General::spell1, Solve::ifun]; s =. ; m =. ; > sols = Solve[{Mean[LogNormalDistribution[m, s]] == mean}, m] > v = Simplify[Variance[LogNormalDistribution[m, s]] /. First[sols]] > Solve[{v == stdev^2}, s]//Simplify > > Bobby > > -----Original Message----- > From: ng [mailto:georgakopoulos at mindspring.com] To: mathgroup at smc.vnet.net > Sent: Thursday, August 08, 2002 5:06 AM > Subject: [mg35959] [mg35923] 4.1 wont Solve LogNormal that 3.x could? > > Why could 3.x sovle the following, while 4.1 considers it unsolvable? > Thanks! > Nicholas > > Off[General::spell1, Solve::ifun]; s =. ;m=.; > sols = Solve[ { > Mean[LogNormalDistribution[m, s]] == mean, > Variance[LogNormalDistribution[m, s]] == stdev^2 > }, {m, s}] ) > > > > >