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Re: wrong result in solving equation and parametric ploting

  • To: mathgroup at smc.vnet.net
  • Subject: [mg111922] Re: wrong result in solving equation and parametric ploting
  • From: Themis Matsoukas <tmatsoukas at me.com>
  • Date: Thu, 19 Aug 2010 07:20:36 -0400 (EDT)

I don't claim to understand the equations you are solving but aren't x,y,z supposed to be real numbers? 

range = 300000000;
intersec = {x, y, z} /. 
   Solve[{1*((x - y)^2 + (y - z)^2 + (z - x)^2)^2 + 
       1000*((x - y)^3 + (y - z)^3 + (z - x)^3)^1 == 2*(250*10^6)^4, 
     0 == x + y + z}, {z, y}];
intersec /. x -> range/10.0

{{3.*10^7, -1.5*10^7 + 1.37486*10^8 I, -1.5*10^7 - 
   1.37486*10^8 I}, {3.*10^7, -1.5*10^7 - 1.37486*10^8 I, -1.5*10^7 + 
   1.37486*10^8 I}, {3.*10^7, 
  1.17486*10^8, -1.47486*10^8}, {3.*10^7, -1.47486*10^8, 
  1.17486*10^8}}

For some values of x (x=0, for example), all roots are complex. Moreover, intersec is not a list of three numbers, as ParametricPlot3D assumes,  but a list of four sets of {x,y,z} roots. It seems to me that you should be choosing the appropriate roots somehow. 

Sorry I can't be of any further help.

Themis


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