Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2010

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

Search the Archive

Re: Imposing constraints on a system of equations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg109367] Re: Imposing constraints on a system of equations
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Fri, 23 Apr 2010 03:50:28 -0400 (EDT)

Just use Reduce instead of Solve:

sols = 
 Reduce[eq1 && eq2 && eq3 && r >= 0 && h >= 0, {r, h, x}, Reals, 
     Backsubstitution -> True]

(a == 0 && r == 0 && h == 0) || (a == 0 && r == 0 && 
      h > 0 && x == 0) || (a > 0 && 
      r == Sqrt[a]/Sqrt[6*Pi] && 
      h == Sqrt[2/(3*Pi)]*Sqrt[a] && 
      x == -(Sqrt[a]/(2*Sqrt[6*Pi])))


On 22 Apr 2010, at 16:31, Virgil Stokes wrote:

> A very simple question on imposing conditions/constraints.
> 
> I know that a, r, and h must be real and non-negative in the following 
> system of equations:
> 
> eq1=Pi*r^2+2*Pi*r*x==0;
> eq2=2*Pi*r*h+(2*Pi*h+4*Pi*r)*x==0;
> eq3=2*Pi*r^2+2*Pi*r*h-a==0;
> sols=Solve[{eq1,eq2,eq3},{r,h,x}]
> 
> How can I impose conditions on this system such that only real solutions 
> are obtained, and r and h are non-negative?
> 
> Thank you,
> --V
> 
> 



  • Prev by Date: Re: Find (cyclic) Sequence
  • Next by Date: Re: Positions of Polynomials in expr?
  • Previous by thread: Re: Imposing constraints on a system of equations
  • Next by thread: Re: Imposing constraints on a system of equations