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

Mathematica calling module from NDSolve

  1. Jul 9, 2013 #1

    I want to use a module to repeatedly calculate a parameter in NDSolve, but I seem to be having trouble. Here is a simplified version of what I'm doing. In this example, I want to use the difference between v1 and v2 at a given timepoint to calculate the connection between v1 and v2 for the next timepoint.

    I am getting the error "NDSolve::ndnum: Encountered non-numerical value for a derivative at s == 0.`." but as far as I can see, everything is defined in the module. If I replace Tau with a constant, I get no errors, which leads me to think it must be something to do with the way I am sampling the value of v1 and v2 from the main NDSolve loop?

    Thanks for your help


    connection[vdiff_, t_] :=
    Module[{deltav = vdiff, Tau, con},

    Tau = 120 + 7434.49/(1 + 0.00262985 (deltav[[1]])^2);

    con = NDSolve[{g' == (1/Tau)*(3 - g), g[0] == 1},
    g, {s, 0, T}];

    g[t] /. con]

    A = 3;
    \[Epsilon] = 0.2;
    \[Alpha] = 3;
    \[Gamma] = 0.05;
    v0 = 0.4;
    w0 = 0.4;
    T = 25;

    initial =
    Solve[wi == A*vi*(vi - \[Alpha])*(1 - vi) - w0 &&
    wi == (vi - v0)/\[Gamma], {vi, wi}, Reals];

    fitz = NDSolve[{v1'[
    t] == ((A*v1[t]*(v1[t] - \[Alpha])*(1 - v1[t]) - w1[t] -
    + (connection[v1[t] - v2[t], t]*(v2[t] - v1[t])),

    v2'[t] == ((A*v2[t]*(v2[t] - \[Alpha])*(1 - v2[t]) - w2[t] -
    + (connection[v2[t] - v1[t], t]*(v1[t] - v2[t])),

    w1'[t] == v1[t] - \[Gamma]*w1[t] - v0,

    w2'[t] == v2[t] - \[Gamma]*w2[t] - v0,

    v1[0] == kick + vi /. initial,
    v2[0] == vi /. initial,
    w1[0] == wi /. initial,
    w2[0] == wi /. initial},

    {v1, v2, w1, w2}, {t, 0, T}];
  2. jcsd
  3. Jul 9, 2013 #2
    NDSolve expects everything, except the function you are solving for and the independent variable, to have been assigned a fixed numeric value.

    When I insert
    Print["Tau=", Tau];
    just after your initialization of Tau in your connection[] module it prints
    Tau=120+7434.49/(1+0.00262985 v1[t]^2)
    and then your NDSolve is going to fail.

    That is why your connection[] NDSolve is throwing an error and then your replacement is throwing an error and then your outer NDSolve is throwing an error.

    See if you can find a way to pass your connection constant Real values and see what happens.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Similar Threads for Mathematica calling module
Mathematica Storing Mathematica output
Mathematica Mathematica to MATLAB
Mathematica Cannot do the integral of the Hyper-geometric function?
Mathematica Cannot Plot This Function in Mathematica
Mathematica While Loop in Mathematica