Re: Repost: Solve: same or new bug?
- To: mathgroup at smc.vnet.net
- Subject: [mg17704] Re: [mg17661] Repost: Solve: same or new bug?
- From: "Andrzej Kozlowski" <andrzej at tuins.ac.jp>
- Date: Sun, 23 May 1999 02:25:24 -0400
- Sender: owner-wri-mathgroup at wolfram.com
This sort of thing was discussed recently. You are quite right, the reason is that Mathematica can only check numerical solutions. I thought it did no checking at all in symbolic cases but as pointed out by Daniel Lichtblau it does do some very basic one. However, clearly it is not something it could be expected to successfully do in general (such verifications are not in general possible) so you shouldn't call this behaviour a bug (though I do think that Mathematica should display a message like "Some or all of the solutions may be spurious"). There are two ways to clear all the variables. The first is to load the CleanSlate package. It defines the command CleanSlate[] which will do this for you. The other way is to quit the Kernel from the Kernel menu and then re-load it again, either from the same menu or by performing a new evaluation. -- Andrzej Kozlowski Toyama International University JAPAN http://sigma.tuins.ac.jp http://eri2.tuins.ac.jp ---------- >From: Thomas Gawlick <Thomas.Gawlick at uni-vechta.de> To: mathgroup at smc.vnet.net >To: mathgroup at smc.vnet.net >Subject: [mg17704] [mg17661] Repost: Solve: same or new bug? >Date: Fri, May 21, 1999, 4:37 PM > > > > > In the following example Mathematica happens to find a "general > solution'" that does not special to a solution for numerical > specialization of the paramters a,e. > > m:=Sqrt[1-a^2] > g:=(x*(a+y)-m*(a+y+e))^2+y^2*(a+y+e)^2-(a+y+e)^2 > gx:=D[g,x] > gy:=D[g,y] > Solve[{g==0,gx==0,gy==0},{x,y}] > {{x -> 0, y -> -a - e}, > {x -> (a*(1 - a^2)^(1/2)*e)/(-1 + a^2), y -> -a}, > {x -> (a*(1 - a^2)^(1/2)*e)/(-1 + a^2), y -> -a}} > % /. {a->.5,e->.1} > {{x -> 0, y -> -0.6}, {x -> -0.057735, y -> -0.5}, > > {x -> -0.057735, y -> -0.5}} > a:=.5; e:=.1 > Solve[{g==0,gx==0,gy==0},{x,y}] > {{x -> 0., y -> -0.6}} > > Is the reason for this that Mathematica checks numerical solutions only? > > Another small question: How do you achieve to clear ALL variables? > > -- > Best regards > > Thomas Gawlick > --- > Dr.rer.nat. Thomas Gawlick > > Hochschulassistent fur Didaktik der Mathematik > > Hochschule Vechta, 49364 Vechta