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MathGroup Archive 2007

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Re: Possible bug in NSolve[equation, variable, precission]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg74391] Re: Possible bug in NSolve[equation, variable, precission]
  • From: dh <dh at metrohm.ch>
  • Date: Mon, 19 Mar 2007 22:04:43 -0500 (EST)
  • References: <etg4m9$ioi$1@smc.vnet.net>


Hi Julian,

Reduce can take a parameter that specifies the domain in which to solve 

the equations. E.g.:

Reduce[poly,x,Reals]

retursn only real solutions.

Daniel





Julian Aguirre wrote:

> Dear group,

> 

> Mathematica 5.2 chokes solving numerically a polynomial equation.

> 

> In[1] := $Version

> Out[1]= 5.2 for Mac OS X (64 bit) (June 20, 2005)

> 

> In[2]:= poly=171142046150220198693105489-16023210221608713837587916

> x-2020825892011586434364754 x^2+190894692033395024364972

> x^3+6039743423966949379761 x^4-568929229651998950400

> x^5-470066550477520896 x^6+2821109907456 x^7;

> 

> In[3]:= poly2=Expand[poly/9];

> 

> In[4]:= NSolve[poly==0,x]

> Out[4]= {-1211.83, -13.0015, -13.0014, 11.923, 12.0809, 12.2509,

> 167826.}

> 

> (* Up to this moment, everything is O.K. But *)

> 

> In[5]:= NSolve[poly==0,x,20]

> Out[5]= $Aborted (* after a loooong time *)

> 

> (* However, the following works as expected*)

> 

> In[6]:= x/.NSolve[poly2==0,x,20]

> Out[6]= {-1211.8267955098487289, -13.001455891126, -13.001441554521,

> 11.92303189062617, 12.08089051352363, 12.25087466630727,

> 167826.26017849924816}

> 

> Let me say that I have used Mathematica to solve thousands (probably

> millions) of equations like the one above. There must be some magic in

> the coefficients!

> 

> Julian Aguirre

> University of the Basque Country

> 

> 




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