Re: Coaxing N[] to work

*To*: mathgroup at smc.vnet.net*Subject*: [mg73404] Re: Coaxing N[] to work*From*: "Steven.Shippee" <slshippee at comcast.net>*Date*: Thu, 15 Feb 2007 05:07:06 -0500 (EST)*References*: <equo6r$in0$1@smc.vnet.net>

On Feb 14, 2:27 am, <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? Whereas you introduced approximations in your original post/problem, Mathematica did not see fit to compute numbers out to the degree of precision you asked for. If you try the following I think you get closer to what you are trying for ... Steven Shippee slshippee at comcast.net In[1]:= x = {2, 3, 5}; A = { {6, 2, 1}, {2, 3, 1}, {1, 1, 1} }; For[k=0,k<15,++k,lambda=x.A.x/(x.x); y=LinearSolve[A,x]; x=y/Norm[y,Infinity];] In[4]:= sol1=lambda Out[4]= \!\(1102158619423970036337\/1903774504398915184457\) In[5]:= N[%,30] Out[5]= 0.578933385691052787623495851172