MathGroup Archive 2003

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Solve real roots only ?

  • To: mathgroup at
  • Subject: [mg43600] Re: [mg43585] Solve real roots only ?
  • From: Andrzej Kozlowski <akoz at>
  • Date: Tue, 23 Sep 2003 04:01:45 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

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

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

  • Prev by Date: Re: package functions in mathlink
  • Next by Date: Mathematica commands needed to solve problem in Set Theory!
  • Previous by thread: Solve real roots only ?
  • Next by thread: Re: Solve real roots only ?