Not enough input arguments, ODE 45, System of ODEs

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Ievgenii
Ievgenii am 25 Okt. 2014
Kommentiert: Star Strider am 26 Okt. 2014
Hello everybody! I seem to be very unlucky, I can not find any solution to my problem - I have:
Error using chu2 (line 9)
Not enough input arguments.
Here is my code:
function dy = chu2(y)
m0 = -3/7;
m1 = 4/7;
alpha = 9;
beta = 14;
dy = zeros(3,1);
dy(1) = alpha*(y(2) - y(1) - (.5)*(m0 - m1)*(abs(y(1) + 1) - abs(y(1) - 1)));
dy(2) = y(1) - y(2) + y(3);
dy(3) = -beta*y(2);
[~,Y] = ode45(@chu2,[0 1 1]);
plot3(Y)
Firstly, I thought the problem is because I gave not enough info, but I have checked everything.
Also I have a question about ODE45 - what method Matlab uses as it ? Runge–Kutta method ?* * Thank you for answering such dull question, but I am so desperate to find any mistake in my code, I have googled but that did not help.
Solution to this problem by Star Strider is to call not the chu2(y) but chu2(~,y)

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Star Strider
Star Strider am 25 Okt. 2014
First, it seems that you are calling your ODE function ‘chu2’ from inside the function, with these lines:
[~,Y] = ode45(@chu2,[0 1 1]);
plot3(Y)
Do not do that! Call it from outside your function, in the main script file.
Second, the ODE solvers require 3 arguments, the first one being your ODE function (that you supplied), the second one being vector containing a range [beginning end] or vector of solution times, and the third your initial conditions. It seems you omitted your time vector, the reason you got the error.
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Ievgenii
Ievgenii am 26 Okt. 2014
Bearbeitet: Ievgenii am 26 Okt. 2014
Here is full code to chu2.m
function dy = chu2( * *!! you mean here I should write input arguments?!!* * )
m0 = -3/7;
m1 = 4/7;
alpha = 9;
beta = 14;
dy = zeros(3,1); % 0 0 0
dy(1) = alpha*(y(2) - y(1) - (1/2)*(m0 - m1)*(abs(y(1) + 1) - abs(y(1) - 1)));
dy(2) = y(1) - y(2) + y(3);
dy(3) = -beta*y(2);
end
And I am calling it in command line like this :
[T,Y] = ode45(@chu2,[0 10],[0 1 1]);
If I write here function dy = chu2( ~,y ) then program has no ERRORs!
One more question - How can plot my system ODE if the output, as far as I understand is: Column vector of time points and Solution array. Each row in Y corresponds to the solution at a time returned in the corresponding row of T. To plot 3d plot I need to have each projection of Y to plot on its own axis, and I will have such numbers (y1,y2,y3) - T times. But how to separate from the Y projections?
Star Strider
Star Strider am 26 Okt. 2014
Quoting:
‘function dy = chu2( * !! you mean here I should write input arguments?!! * )’
Yes!
‘If I write here function dy = chu2( ~,y ) then program has no ERRORs!’
Success!!
If you want to plot each y-value on its own axis, I would use the subplot function:
figure(1)
subplot(2,1,1)
plot(t, y(:,1))
title('Y_1')
grid
subplot(2,1,2)
plot(t, y(:,2))
title('Y_2')
grid
subplot(2,1,3)
plot(t, y(:,3))
title('Y_3')
grid
That should work for your plots.

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