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
>
>