Re: Emergent Help: NSolve Problems!

*To*: mathgroup at smc.vnet.net*Subject*: [mg39776] Re: Emergent Help: NSolve Problems!*From*: Alois Steindl <Alois.Steindl at jet2web.cc>*Date*: Fri, 7 Mar 2003 03:30:46 -0500 (EST)*Organization*: Inst. f. Mechanics II, TU Vienna*References*: <b46tqk$91h$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Chengzhou Wang <wcz at ece.ucsd.edu> writes: > Hi, guys > > I have some complicated polynomials, and I want to calculate its roots. > HOwever, when I use NSolve, it creates some problems. Say a simple > example: > > temp[s_]=s^10+10 s^9+ 10 s^8 +10 s^7 +10 s^6+ 10 s^5 +10 s^4 +1; > NSolve[temp[s]==0, s] > > It will give: > > Out[4]= {{s -> -8.99998}, ...} > > But when I plug in the first number, which is "-8.99998", it should give a > value close to zero. However, it gives: > > In[5]:= temp[-8.99998] > Out[5]= -411.473 > > The other roots seems OK. Does anyone know why? This is just a simple > example. I have some more complicated polynomials to deal with. > Hello, If you do xs = NSolve[temp[s] == 0, s] temp[s /. First[xs]] you will get a number very close to 0. Did you check the derivative of temp at this point? You might need to consult the chapters about Precision. > PS: Please reply (cc) to my email. I did not subscribe my email to the > this email group! > No, no. Post here, read here. Alois