??? Undefined function or variable 'ODE45_main'.

A case of matlab :

ODE45_fun.m function dy=ODE45_fun(t,y) a=1;b=1;c=9;

dy(1)=-a*y(1)+y(3)*y(2); dy(2)=-b*(y(1)+y(3)); dy(3)=c*y(2)-y(3)-3*y(2)*y(1);

dx=[dx(1);dx(2);dx(3)];

and ODE45_main.m

tspan=[0,100]; y0=[0;0;10^(-10)]; [t,y]=ode45('ODE45_fun',tspan,y0); data=[t,y]; save ODE45_data.txt data-ascii plot3(y(:,1),y(:,2),y(:,2)) grid on title('Lorenz 方程')

>> ODE45_main

Now： ??? Undefined function or variable 'ODE45_main'.

Answer 1

[John D'Errico]

The obvious questions apply here.

1. Did you save it as an m-file?
2. On your search path?
3. Where on your search path?

Please do this:

which ODE45_main

Note that too often, the answer to the last question is the person has saved the function into the MATLAB directories. Bad idea.