Not enough input arguments. in ode45

Hi,

I am trying to run the code given as an example on mathworks website (https://www.mathworks.com/help/matlab/ref/ode45.html) for ode45 and still it is giving me the error saying : "Not enough input arguments"

This is the code:

function dydt = vdp1(m,y)
dydt = [y(2); (1-y(1)^2)*y(2)-y(1)];

[m,y] = ode45(@vdp1,[0 20],[2; 0]);
plot(m,y(:,1),'-o',m,y(:,2),'-o')
title('Solution of van der Pol Equation (\mu = 1) with ODE45');
xlabel('Time t');
ylabel('Solution y');
legend('y_1','y_2')

I am trying this as I am developing a new code based on this template and that is not working either.

What can I do?

[Star Strider]

The code you posted runs without error for me, and produces the appropriate plot.

[KALYAN ACHARJYA]

@Star

function dydt = vdp1(m,y)
%....................^ inputs 
dydt = [y(2); (1-y(1)^2)*y(2)-y(1)];
[m,y] = ode45(@vdp1,[0 20],[2; 0]
%^^   again calculating m and y?? 

[Star Strider]

I changed it only to use the anonymous function version of ‘vdp1’ (and the appropriate reference to it in the ode45 call) and it ran without error:

vdp1 = @(m,y) [y(2); (1-y(1)^2)*y(2)-y(1)];

[m,y] = ode45(vdp1,[0 20],[2; 0]);
plot(m,y(:,1),'-o',m,y(:,2),'-o')
title('Solution of van der Pol Equation (\mu = 1) with ODE45');
xlabel('Time t');
ylabel('Solution y');
legend('y_1','y_2')

The first argument to a function the ODE solvers use is the dependent variable (usually ‘t’, here ‘m’), and the second is the dependent variable, here ‘y’. The code is correct and runs without error.

We are not seeing the code that is throwing the error, so it is not possible to figure out what the problem is.

[Steve]

Thank you--the 2nd version given by Star Strider does work on my machine. However, the 1st version does not. I believe it has to do with the name my program is stored under.

I apparently need to study the instructions for using handles.

Answer 1

[madhan ravi]

[m,y] = ode45(@vdp1,[0 20],[2; 0]);
plot(m,y(:,1),'-o',m,y(:,2),'-o')
title('Solution of van der Pol Equation (\mu = 1) with ODE45');
xlabel('Time t');
ylabel('Solution y');
legend('y_1','y_2')
% try the above in command window or in a separate script file
% ------------
function dydt = vdp1(m,y) % save this in a separate file named as vdp1.m
dydt = ...;

[minu pilvankar]

Thanks for the response! Yeah, thats what I thought coz it ran fine on my lab computer. Not sure what is wrong then.

[madhan ravi]

https://in.mathworks.com/help/matlab/ref/function.html#description - read the second point