[Date Index]
[Thread Index]
[Author Index]
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
Prev by Date:
**Re: producing a noise**
Next by Date:
**Re: ReplacePart -> eliminate**
Previous by thread:
**Re: very odd failure of Solve**
Next by thread:
**Re: very odd failure of Solve**
| |