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MathGroup Archive 2007

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Possible bug in NSolve[equation, variable, precission]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg74299] Possible bug in NSolve[equation, variable, precission]
  • From: "Julian Aguirre" <julian.aguirre at ehu.es>
  • Date: Sat, 17 Mar 2007 02:10:24 -0500 (EST)

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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