ode45 for third order differential

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Nikola Otic
Nikola Otic 2018-4-26
评论： Star Strider 2018-4-26
I am trying to solve a third order differential equation by representing it as a set of first order diff equations. The constants are user input arguments.
A=str2double(get(handles.Avalue, 'string'));
B=str2double(get(handles.Bvalue, 'string'));
C=str2double(get(handles.Cvalue, 'string'));
E=str2double(get(handles.Evalue, 'string'));
F=str2double(get(handles.Fvalue, 'string'));
t=str2double(get(handles.tvalue, 'string'));
xinitial=0;
where t is the final value on the x axis
[T,X] = ode45(@funsys, [0 t], [0 0 0 0]);
plot(T, X(:,1), 'Parent', handles.axes1)
plot(T, X(:,2), 'Parent', handles.axes2)
plot(T, X(:,3), 'Parent', handles.axes3)
plot3(X(:,1),X(:,2),X(:,3), 'Parent', handles.axes4)
I am using the following function stored in a separate m file
function diff_f=funsys(t,x,A,B,C,E,F)
diff_f=zeros(4,1);
diff_f(1)=x(2);
diff_f(2)=x(3);
diff_f(3)=x(4);
diff_f(4)=(F*exp(-0.1*t)*cos(t)+B*x(4)-C*t*x(3)+E*x(2))/A;
end
Whenever I run it I receive an error message:
Not enough input arguments.
Error in funsys (line 7)
diff_f(4)=(F*exp(-0.1*t)*cos(t)+B*x(4)-C*t*x(3)+E*x(2))/A;
I tried using syms x to see if x is the problem, otherwise all other arguments are present.

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