Re: Coaxing N[] to work
- To: mathgroup at smc.vnet.net
- Subject: [mg73398] Re: [mg73370] Coaxing N[] to work
- From: "Igor C. Antonio" <igora at wolf-ram.com>
- Date: Thu, 15 Feb 2007 05:03:50 -0500 (EST)
- Organization: Wolfram Research, Inc.
- References: <200702141020.FAA19038@smc.vnet.net>
- Reply-to: igora at wolf-ram.com
p at dirac.org wrote: > Sometimes N[,] doesn't appear to work. Like here: > > > x = {2.0, 3.0, 5.0}; > A = { {6.0, 2.0, 1.0}, {2.0, 3.0, 1.0}, {1.0, 1.0, 1.0} }; > For[ k=0, k<15, ++k, > lambda = x.A.x/(x.x); > y = LinearSolve[A,x]; > x = y / Norm[y,Infinity]; > ] > N[lambda, 30] > > > The output is: > > Out[5]= 0.578933 > > I was expecting 30 digits. Why did N[] ignore my request for 30 digits? PLEASE read the documentation before posting to the newsgroup. The very first line of the docs for N[] says: "Unless numbers in expr are exact, or of sufficiently high precision, N[expr, n] may not be able to give results with nâ??digit precision." In[1]:= x={2/10,3/10,5/10}; A={{6/10,2/10,1/10},{2/10,3/10,1/10},{1/10,1/10,1/10}}; For[k=0,k<15,++k,lambda=x.A.x/(x.x); y=LinearSolve[A,x]; x=y/Norm[y,Infinity];] N[lambda,30] Out[4]= 0.0578933385691052787623495851172 -- Igor C. Antonio Wolfram Research, Inc. http://www.wolfram.com To email me personally, remove the dash.
- References:
- Coaxing N[] to work
- From: <p@dirac.org>
- Coaxing N[] to work