Error Message Using ODE45

The following code was copied directly from MatLab ODE45 documentation into MatLab script:

function dydt = vdp1(t,y)
%VDP1  Evaluate the van der Pol ODEs for mu = 1
%   See also ODE113, ODE23, ODE45.
%   Copyright 1984-2014 The MathWorks, Inc.
dydt = [y(2); (1-y(1)^2)*y(2)-y(1)];
[t,y] = ode45(@vdp1,[0 20],[2; 0]);
plot(t,y(:,1),'-o',t,y(:,2),'-o')

The error message received from RUN execution is:

>> vdp1
Not enough input arguments.
Error in vdp1 (line 7)
dydt = [y(2); (1-y(1)^2)*y(2)-y(1)];

Is there a solution or work around for this issue?

Answer 1

[Walter Roberson]

The part starting from

[t,y] = ode45(@vdp1,[0 20],[2; 0]);
plot(t,y(:,1),'-o',t,y(:,2),'-o')

Should be in a different file that is the one to be run.

Answer 2

[Eugene Dirk]

Hello,

The proposed solution did not work; no other 'y' was found in the directory. The function defined in the original message was placed in a directory by itself and results of execution (free from any 'y' ) failed. After some some rework of the MatLab code, the following solution (below) produced the correct results.

function  vdp1
 %VDP1  Evaluate the van der Pol ODEs for mu = 1
%
%   See also ODE113, ODE23, ODE45.
%   Copyright 1984-2014 The MathWorks, Inc.
[t,y] = ode45(@(t,y) [y(2); (1-y(1)^2)*y(2)-y(1)], [0 20],[2; 0]);
plot(t,y(:,1),'-o',t,y(:,2),'-+')

Thank you for your prompt response to my problem. With the work around above, the class of problems I will be working on can be handled satisfactorily.

Answer 3

[Eugene Dirk]

Heloo Walter,

Thanks for your suggestion-unfortunately, it did not work. However, I rewrote the MatLab code, shown below, that did execute successfully.

function vdp1
%VDP1  Evaluate the van der Pol ODEs for mu = 1
%
%   See also ODE113, ODE23, ODE45.
%   Copyright 1984-2014 The MathWorks, Inc.
[t,y] = ode45(@(t,y) [y(2); (1-y(1)^2)*y(2)-y(1)], [0 20],[2; 0]);
plot(t,y(:,1),'-o',t,y(:,2),'-+')

Again, thanks for the input.

Gene

[darova]

Great work, thanks! It works!

Answer 4

[Eugene Dirk]

Hello,

Unfortunately, the suggested resolutions to the problem I posed did not work. I supplied the solution that finally resolved the issue with ode45 that was encountered in my particular case.

Again, thanks to everyone who provided suggestions for solving my problem. I understand that not every suggestion works, but please keep trying to help people like myself that encounter MatLab issues.

Gene