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MATLAB help-ode45

  1. Aug 26, 2011 #1
    Hello,

    I am trying to write a program on matlab using ode45 to solve the following equations:

    S'=-bSZ-sS
    Z'=bSZ+gR-aSZ
    R'=sS+aSZ-gR

    These are all derivatives with respect to t, differential equations.

    a, b, a and g are all constants.

    I realise I need to have two m files, one which defines the functions, and one which calls that and uses ode45. The code for my first m file is:


    function Yout = program1(S,Z,R);

    global beta gamma alpha sigma;

    % set the parmeter values
    tend = 10;
    S0 = 500;
    I0 = 1;
    b=0.0095;
    g=0.0001;
    a= 0.005;
    s=0.0001;

    Sdot=(-b)*S*Z-(gg*S);

    Zdot=(b*S*Z)+(g*R)-(a*S*Z);

    Rdot=(s*S)+(a*S*Z)-(g*R);

    udot = [Sdot; Zdot; Rdot];

    I'm not sure if that is suitable, and I also need help writing the second m file. I need to plot Z and R on the same plot, vs t. I am really stuck, I have been working for hours, looking at examples, trying different combinations. MATLAB is most definitely not my strong point.

    Thanks for the help!
     
  2. jcsd
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