What was that problem?

Matlab：edit，then add the the following values in a m.file

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    function dx=myfun(t,x)
    dx(1)=-6*x(2)*x(2)-9;
    dx(2)=-3*x(1)*x(2)-2*x(3)-Yvv-Yuu;
    dx(3)=x(1)*x(2)+x(3)+8;
    Yvv=0.5*p*L*T*(0.048265-6.293*(1-c)*T/B);
    Yuu=0.5*p*L*L*L*T*(0.0045-0.445*(1-c)*T/B);
    dx=dx(:);
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Finally,， Matlab ：

    clear all
    clc
    syms Yvv Yuu p L T c T B 
    x0=[1,1,1];
    t0=0:0.1:2;
    [t,x]=ode45('myfun',[0,10],x0);  %ode45会自动调整步长
    plot(t,x) 
    legend('u','v','Y')

Answer 1

[Torsten]

Try

      %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
      function dx=myfun(t,x)
      p=1;
      L=1;
      T=1;
      c=1;
      B=1;
      Yvv=0.5*p*L*T*(0.048265-6.293*(1-c)*T/B);
      Yuu=0.5*p*L*L*L*T*(0.0045-0.445*(1-c)*T/B);
      dx(1,1)=-6*x(2)*x(2)-9;
      dx(2,1)=-3*x(1)*x(2)-2*x(3)-Yvv-Yuu;
      dx(3,1)=x(1)*x(2)+x(3)+8;
      %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

      clear all
      clc
      x0=[1,1,1];
      t0=0:0.1:2;
      [t,x]=ode45('myfun',[0,10],x0);  %ode45会自动调整步长
      plot(t,x) 
      legend('u','v','Y')

Best wishes

Torsten.

[Lan]

p=L=T=c=B=1

why ？

[Torsten]

Because you have to give numerical values to them instead of defining them as symbolic variables. ODE45 can not handle symbolic variables.

Best wishes

Torsten.

[Lan]

There are another two questions, would you help me ?