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WHY do I get this error

Asked by mahesh tom on 17 Nov 2017
Latest activity Edited by mahesh tom on 17 Nov 2017
function dydt = free25(t,y);
g = 9.81;
l = 1;
dydt = [y(2);-g/l.*sin(y(1))];
end
[t,y]= ode45('free25',[0 10],[0 0.09]);%I typed this in command window
plot(t,y(:,1));
refline([0 0]);
Error using feval Undefined function 'free25' for input arguments of type 'double'.
Error in odearguments (line 87) f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.
Error in ode45 (line 115) odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

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1 Answer

Answer by Mischa Kim
on 17 Nov 2017
Edited by Mischa Kim
on 17 Nov 2017
 Accepted Answer

mahesh, is the above code all in one and the same script? If it is modify like this:
[t,y]= ode45(@free25,[0 10],[0 0.09]);%I typed this in command window
plot(t,y(:,1))
function dydt = free25(t,y)
g = 9.81;
l = 1;
dydt = [y(2);-g/l.*sin(y(1))];
end
Another option would be to store the first part of the script (first two commands) in one function and the second part in a different function. For this second option make sure you name the file the same way you name the function: free25.m

  3 Comments

no..i have saved free25 as a separate .m file
OK. Name of the file needs to be free25.m. In the command window type
[t,y] = ode45(@free25,[0 10],[0 0.09]);%I typed this in command window
and make sure the file is in the current folder (see folder window in MATLAB) or on in a folder that is in the MATLAB search path.
Thank you! The problem was that the file was not on the MATLAB search path!

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