Re: System for which Solve and NSolve both fail
- To: mathgroup at smc.vnet.net
- Subject: [mg30650] Re: System for which Solve and NSolve both fail
- From: Ben Langton <ben at quickmath.com>
- Date: Sun, 2 Sep 2001 03:58:56 -0400 (EDT)
- References: <9mi1rt$54r$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Thanks for your helpful replies, everyone. Would I be correct in concluding that Solve (or NSolve for higher degree systems) will always produce at least a numerical approximation of the complete solution set for a system of polynomial equations, but is not guaranteed to do so for non-polynomial systems? Also, is there any reliable predictor of which non-polynomial systems these commands will fail on (I'm guessing not, since otherwise WRI would use such a predictor to extend their software to deal with these cases)? I know this is probably getting a bit esoteric, but if anyone could shed some light on why these commands work for some non-polynomial systems but not others, I would be very interested to find out more. Regards, Ben Langton, QuickMath > From: Ben Langton <ben at spam.bugs.me.quickmath.com> To: mathgroup at smc.vnet.net > Organization: OzEmail Ltd, Australia > Newsgroups: comp.soft-sys.math.mathematica > Date: Wed, 29 Aug 2001 06:25:01 +0000 (UTC) > Subject: [mg30650] System for which Solve and NSolve both fail > > Hi, > > I noticed that Mathematica seems unable to solve this system of equations : > > 3^x + 3^y = 90 > > x + y = 6 > > With a bit of thought, you can see by inspection that the solutions are > > {x , y} = {2 , 4} or {4 , 2} > > However, when I use the commands > > Solve[{3^x+3^y==90,x+y==6},{x,y}] > > or > > NSolve[{3^x+3^y==90,x+y==6},{x,y}] > > I get a warning message starting with > > Solve::incnst: Inconsistent or redundant transcendental equation > > Can anyone shed some light on what is going on here? Any way to get around > this problem? > > (I am using Mathematica v 3.0.0.0 under Mac OS 9.2.1, although I believe a > similar thing occurs under v 4.x) > > Regards, > > Ben Langton > > http://www.quickmath.com/ >