Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Mathematica NDsolve error, ndode?

  1. Jul 22, 2011 #1
    Hi all,

    So I'm trying to solve, what I think are three coupled PDEs with NDSolve and it keeps giving me

    NDSolve::ndode: Input is not an ordinary differential equation. >>

    as an error. I don't quite understand why?

    These are my PDEs for anyone that's interested. I will try to pretty them up in a separate post. I'm kind of in a rush right now.

    Any suggestions/comments about this errors and my PDEs are greatly appreciated. Thank you so much.


    sol = NDSolve[

    {
    D[\[Delta]ur[r, \[Theta]], r] + D[\[Delta]u\[Theta][ r, \[Theta]], \[Theta]] ==
    (ut/ rmd[r, \[Theta]] *(\[Sigma] - m*\[CapitalOmega])*\[Delta]rmd [
    r, \[Theta]] ) - (2/r +
    1/rmd[r, \[Theta]]* drmdr[r, \[Theta]] +
    2*dalphar[r, \[Theta]] + dbetar[r, \[Theta]] +
    dnur[r, \[Theta]])*\[Delta]ur[
    r, \[Theta]] - (Cot[\[Theta]] +
    1/rmd[r, \[Theta]]*drmd\[Theta][r, \[Theta]] +
    2*dalpha\[Theta][r, \[Theta]] + dbeta\[Theta][r, \[Theta]] +
    dnu\[Theta][r, \[Theta]])*\[Delta]u\[Theta][
    r, \[Theta]] + (\[Sigma]*F[r, \[Theta]] -
    m)*\[Delta]u\[CurlyPhi][r, \[Theta]],

    D[\[Delta]p[r, \[Theta]],
    r] == (((\[Epsilon] + p)*ut)/
    Exp [-2 \[Alpha]])*(((1 /(\[Epsilon] + p)^2) *
    Exp [-2 \[Alpha]]/ut *
    D[p[r, \[Theta]],
    r]*(\[Delta]\[Epsilon][r, \[Theta]] + \[Delta]p[
    r, \[Theta]])) - (\[Sigma] -
    m*\[CapitalOmega])*\[Delta]ur[
    r, \[Theta]] + (Exp[2 \[Beta] - 2 \[Alpha]]*
    r^2* (Sin[\[Theta]])^2* ( \[CapitalOmega] - \[Omega][r, q])*
    D[Log [F[r, \[Theta]]], r]* \[Delta]u\[CurlyPhi][
    r, \[Theta]])),

    D[\[Delta]p[
    r, \[Theta]], \[Theta]] == (((\[Epsilon] + p)*r^2 * ut )/
    Exp [-2 \[Alpha]])*((1 /(\[Epsilon] + p)^2 *
    Exp [-2 \[Alpha]]/r^2*ut *
    D[p[r, \[Theta]], \[Theta]]*(\[Delta]\[Epsilon][
    r, \[Theta]] + \[Delta]p[r, \[Theta]]) - (\[Sigma] -
    m*\[CapitalOmega])*\[Delta]u\[Theta][
    r, \[Theta]] + (Exp[2 \[Beta] - 2 \[Alpha]]*
    r^2* (Sin[\[Theta]])^2* ( \[CapitalOmega] - \[Omega][
    r, \[Theta]])*
    D[Log[ F[r, \[Theta]]], r])* \[Delta]u\[CurlyPhi][
    r, \[Theta]])),


    (*Boundary Conditions*)
    \[Delta]\[Theta][1, \[Theta]] ==
    0, \[Delta]ur[1, \[Theta]] == \[Delta]p[
    1, \[Theta]] == \[Delta]\[Theta][r, 1] == \[Delta]ur[r,
    1] == \[Delta]p[r, 1] ==
    0, -I*\[Gamma]1*\[Delta]p[128, \[Theta]] + \[Delta]ur[
    128, \[Theta]]*
    Evaluate[D[\[Delta]p[128, \[Theta]], r]] + \[Delta]u\[Theta][
    128, \[Theta]]*
    Evaluate[D[\[Delta]p[128, \[Theta]], \[Theta]]] ==
    0},

    (*what I'm solving for, and the bounds*)
    {\[Delta]p, \[Delta]ur, \[Delta]u\[Theta]}, {r, 1,
    128}, {\[Theta], 1, 64}]
     
  2. jcsd
  3. Jul 22, 2011 #2
    I cannot tell from what you have shown whether
    1: you have left out a variety of function definitions and variable assignments or
    2: you are thinking NDSolve is going to give you a numeric solution with those undefined.
    If you have defined and assigned all those values so this is strictly a numerical solution process then perhaps the problem lies in what you have not included. If you have not defined and assigned then this is a common problem, people expecting a numerical integration solution when they arbitrary variables or, even worse, arbitrary functions in what they pass to NDSolve nor NSolve.

    From a different direction, it appears that for years people have asked why they are getting this warning message
    http://www.google.com/search?q=Mathematica+"Input+is+not+an+ordinary+differential+equation"
    and there does not appear to be a simple clear answer to that question.

    Does any of this seem to relate to your question?
     
  4. Jul 24, 2011 #3
    Hi Bill,

    I'm very sorry about the lack of explanation. I have added a .pdf file with an explanation of the variables and I've made the eqs nicer.

    I did try looking it up on the google. And I reached the conclusion that no one really knows what causes this error. That's one of the reason's I'm putting it up here. Because I think that I just need someone experience with Mathematica to look at it.


    Thanks again for even looking at this mess. I truly appreciate it.
     

    Attached Files:

  5. Jul 25, 2011 #4
    It isn't easy to import the equations out of a pdf document back into a notebook.

    Would it be possible for you to take all your data and crunch it down to
    Alpha=youractualvalue;
    CapitalOmega=youractualvalue;
    etc
    for all the variables that you actually have values for
    and then prepend onto your latest version of your code
    and attach the resulting notebook to your next post?

    That would let me try to reproduce what you are doing with the actual values you have.
     
  6. Nov 21, 2011 #5
    Hi Bill,

    Really sorry about the late reply. I wasn't sure how to respond. I don't think I can give out the data as this pertains to current research being done.

    I have made some progress on the problem. And I believe one of the problems I was having with Mathematica was not with Mathematica at all. I was just trying to have it solve a problem that was mathematically ill-posed. So its no wonder it failed.

    Anyways, thanks for all the help. Sorry again about the super-late reply.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook