Re: Solve real roots only ?
- To: mathgroup at smc.vnet.net
- Subject: [mg43600] Re: [mg43585] Solve real roots only ?
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Tue, 23 Sep 2003 04:01:45 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
RealOnly is not for this purpose (in fact it's a fairly useless package for people who do not wish to see complex number and are satisfied with simply not getting any answer when these are needed). Solve can't find real roots only. In any case, since your equation involves a parameter it does not make sense to speak of a "real root". Whether a root is real or not depends on the parameter, thus a I is of course real if a is purely imaginary. And by the way, there are real expressions involving radicals which can't be written at all in radical form without using I. Andrzej Kozlowski Yokohama, Japan http://www.mimuw.edu.pl/~akoz/ http://platon.c.u-tokyo.ac.jp/andrzej/ On Monday, September 22, 2003, at 04:14 PM, Pavel Pokorny wrote: > > Dear Mathematica friends, > > how can I tell Solve to find real roots only? > I tried RealOnly but it makes this little program to crash! > > Needs["Miscellaneous`RealOnly`"]; > f = a - (1-x) Sqrt[20 x - 20000 y]; > g = (a(1-y)- 1000 y (1-x))/(10-x); > s = Solve [ f==0 && g==0, {x,y}]; > xs = x /. s; > xx = Series [xs, {a,0,2}]; > > Is it my fault? > > Thanks > > -- > Pavel Pokorny > Math Dept, Prague Institute of Chemical Technology > http://www.vscht.cz/mat/Pavel.Pokorny > > >