What was that problem?

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Lan
Lan 2015-2-10
评论： Lan 2015-2-10
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')

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采纳的回答

Torsten
Torsten 2015-2-10
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.
  3 个评论
显示 1更早的评论
Torsten
Torsten 2015-2-10
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
Lan 2015-2-10
There are another two questions, would you help me ?

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