MathGroup Archive 2001

[Date Index] [Thread Index] [Author Index]

Search the Archive

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

  • To: mathgroup at
  • Subject: [mg29085] Re: Why can't Nsolve find a solution to this ?
  • From: David Kirkby <REMOOVE_THIS_drkirkby at>
  • Date: Sun, 27 May 2001 18:04:50 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

   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. 

Dr. David Kirkby Ph.D,
email: REMOOVE_THIS_drkirkby at 
former email address: davek at
web page:       
Amateur radio callsign: G8WRB

  • Prev by Date: Re: Forcing numbers to be real.
  • Next by Date: Re: Newbie solving mod M linear equations
  • Previous by thread: NonlinearFit work but NonlinearRegress, why?
  • Next by thread: Re: Re: Why can't Nsolve find a solution to this ?