Re: Re: Why can't Nsolve find a solution to this ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg29091] Re: [mg29085] Re: Why can't Nsolve find a solution to this ?*From*: Andrzej Kozlowski <andrzej at tuins.ac.jp>*Date*: Tue, 29 May 2001 02:57:19 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Yes, you are certainly missing something here. NSolve like solve is primarily intended for solving algebraic equations. In yoour case what you need is FindRoot. In[1]:= FindRoot[{1.7863852^2== u^2 + v^2 , u Tan[u] == v}, {u,1},{v,1}] Out[1]= {u -> 0.986055, v -> 1.48959} -- Andrzej Kozlowski Toyama International University JAPAN http://platon.c.u-tokyo.ac.jp/andrzej/ http://sigma.tuins.ac.jp/~andrzej/ on 01.5.28 7:04 AM, David Kirkby at REMOOVE_THIS_drkirkby at AND_THIS_ntlworld.com wrote: > > I'd like if possible to obtain an analytical solution to the > following two simultaneous equations, but given that is apparently not > likely to be found, I thought of a using NSolve to get a numerical one. > However, Nsolve can't seem to find a solution, despite the fact that if > I write a computer programme in 5 minutes or less to solve it > numerically. Am I missing something here ?? > > The equations arrise from optical waveguides: > W^2=u^2 + v^2 > v=u tan(u) > > W is known in advance, so I want to find the 2 variables u and v using > the above 2 equations. I've tried: > > In[2]:= NSolve[ {1.7863852^2== v^2 + u^2, u Tan[u] == v},{u,v}] > > Solve::tdep: The equations appear to involve the variables to be solved > for in > an essentially non-algebraic way. > > 2 2 > Out[2]= NSolve[{3.19117 == u + v , u Tan[u] == v}, {u, v}] > > Yet I know there is a solution to this : u->0.986, v->1.4893. > > Any suggestions on how to get Mathematica to find such solutions ??? > > I'm using Mathematica 4.01 on a Sun SPARCstation 20, with Solaris 8.