Re: very odd failure of Solve

*To*: mathgroup at smc.vnet.net*Subject*: [mg131658] Re: very odd failure of Solve*From*: "Dr. Wolfgang Hintze" <weh at snafu.de>*Date*: Tue, 17 Sep 2013 21:33:52 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-outx@smc.vnet.net*Delivered-to*: mathgroup-newsendx@smc.vnet.net*References*: <l1446c$psj$1@smc.vnet.net> <l16e0j$2g3$1@smc.vnet.net>

Am Montag, 16. September 2013 10:03:31 UTC+2 schrieb Richard Fateman: > On 9/15/2013 4:03 AM, Alan wrote: > > > Setting an irrelevant parameter to 0 baffles Solve. Why? > > > Thanks, > > > Alan Isaac > > > > > > $Assumptions =. > > > ClearAll[f1] > > > f1[x_] := s*x^\[Alpha] - (a + b + c)*x > > > Solve[f1[x] == 0, x] (* Solve works *) > > > Solve[(f1[x] /. {b -> 0}) == 0, x] (* Solve fails *) > > <snip> > > > > Running Reduce[ {%==0}, {x} ] on either equation seems to go into > > an infinite loop. That maybe be an independent bug, though. > > > > I expected that somehow fiddling with the variable names would > > do something, and that the ordering of a,b,c, alpha was critical. > > Out of curiosity I tried a few variants to generate a better > > hypothesis, but ran out of, um, curiosity. Still a bit curious I tried 1) the number miracle Solve[s*x^\[Alpha] - (a + b + c)*x, x] (* Solve works *) Solve[s*x^\[Alpha] - (a + b )*x, x] (* Solve fails *) Solve[s*x^\[Alpha] - (a )*x, x] (* Solve works *) oops, size matters (1 and 3 is okay, 2 not) 2) the simplest case The most simple case of this type in which Solve fails seems to be Solve[x^E - 2*x == 0, x] Solve::nsmet: This system cannot be solved with the methods available to Solve. >> You can safely replace the irrational E by the algebraic Sqrt[2] or other constants apart from rationals. Solve will fail as well. Competition is open to find the simplest case Solve can't do with. Best regards, Wolfgang