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Second Order Differential Equations in MatLab

  1. Aug 5, 2010 #1
    Hey guys, I am new to PF. I need to be able to model a stiff differential equation in MatLab. I haven't used MatLab before so I am not really sure how to set the function and boundary conditions for the equation:

    y'' + (2/x)*Y' = (.7/x^2)*( (y^(-1/2)) - (.067)((1-y)^(-1/2) )

    The zero boundary is undefined and there is a lot of singularities in the solution itself.

    So far I have:

    function dy = f(x,y)
    y = [1 1];
    k = .7;
    lambda = .67;
    xspan = [0 10];
    ic = [0 1];
    dy=[y(2); (-2/x) * y(2) + (k/(x)^2)*( (y(1)^(-1/2)) - lambda*((1-y(1)))^(-1/2) )];
    [x,y] = ode15s(@f,xspan,ic);

    And I am getting a an error in the command console:

    ??? Input argument "x" is undefined.

    Error in ==> f at 7
    dy=[y(2); (-2/x) * y(2) + (k/(x)^2)*( (y(1)^(-1/2)) -
    lambda*((1-y(1)))^(-1/2) )];

    I do not know where to go from here.
  2. jcsd
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