Re: Simultaneous equation solve taking ages

*To*: mathgroup at smc.vnet.net*Subject*: [mg114371] Re: Simultaneous equation solve taking ages*From*: Daniel Lichtblau <danl at wolfram.com>*Date*: Thu, 2 Dec 2010 05:40:50 -0500 (EST)

Peter Bone wrote: > I'm trying to execute this solve. I ran it for 5 hours and it hasn't > finished yet. Will this ever finish? Why is it taking so long? > > Solve[a^2 == d^2 + f^2 - 2*d*f*x && b^2 == e^2 + f^2 - 2*e*f*y && c^2 > == d^2 + e^2 - 2*d*e*z, {d, e, f}] > > I haven't used Mathematica much before so I'm not sure I've done it > correctly. This is for a geometrical problem involving 3 cosine rule > equations. a, b, c, x, y, z are known. Trying to find d, e, f in terms > of the knowns. > > Pete In Mathematica 8: In[38]:= polys = {-a^2 + d^2 + f^2 - 2*d*f*x, -b^2 + e^2 + f^2 - 2*e*f*y, -c^2 + d^2 + e^2 - 2*d*e*z}; In[46]:= Timing[ soln = Solve[polys == 0, {d, e, f}, Cubics -> False, Quartics -> False];] Out[46]= {15.1117, Null} In[48]:= LeafCount[soln] Out[48]= 29163433 At this point I would raise the question of how badly you really want this solution? Daniel Lichtblau Wolfram Research