How to Call a Function Within a Script?

Hi everyone,

Still learning Matlab. I am trying to solve replicate a script on MathWorks website. The function on MathWorks website is shown below:

function dydt = vdp1000(t,y)
%VDP1000  Evaluate the van der Pol ODEs for mu = 1000.
%
%   See also ODE15S, ODE23S, ODE23T, ODE23TB.

%   Jacek Kierzenka and Lawrence F. Shampine
%   Copyright 1984-2014 The MathWorks, Inc.

dydt = [y(2); 1000*(1-y(1)^2)*y(2)-y(1)];

[t,y] = ode15s(@vdp1000,[0 3000],[2 0]);
plot(t,y(:,1),'-o')

However, when I run, I get an error "not enough input parameters, error in dydt = [y(2); 1000*(1-y(1)^2)*y(2)-y(1)];

I am able to get it to work when I run this part below separately and remove it from the code above...meaning two separate m files.

[t,y] = ode15s(@vdp1000,[0 3000],[2 0]);
plot(t,y(:,1),'-o')

Question is how do I get the code/function above to work without running the lines below separately? Thank you!

[t,y] = ode15s(@vdp1000,[0 3000],[2 0]);
plot(t,y(:,1),'-o')

Answer 1

[Torsten]

You have two options:

Either define your derivatives in a function:

[t,y] = ode15s(@vdp1000,[0 3000],[2 0]);
plot(t,y(:,1),'-o')

function dydt = vdp1000(t,y)
%VDP1000  Evaluate the van der Pol ODEs for mu = 1000.
%
%   See also ODE15S, ODE23S, ODE23T, ODE23TB.
%   Jacek Kierzenka and Lawrence F. Shampine
%   Copyright 1984-2014 The MathWorks, Inc.
dydt = [y(2); 1000*(1-y(1)^2)*y(2)-y(1)];
end

or you define your derivatives by a function handle directly in the script:

vdp100 = @(t,y)[y(2); 1000*(1-y(1)^2)*y(2)-y(1)];
[t,y] = ode15s(vdp100,[0 3000],[2 0]);
plot(t,y(:,1),'-o')

Answer 2

[David Hill]

%execute function
dydt=vdp1000(t,y);%must assign t and y prior to executing the function


function dydt = vdp1000(t,y)
dydt = [y(2); 1000*(1-y(1)^2)*y(2)-y(1)];
[t,y] = ode15s(@vdp1000,[0 3000],[2 0]);
plot(t,y(:,1),'-o')
end

Answer 3

[Cris LaPierre]

Here is how you run the example you mention. Note that the last 2 lines of code in the example are how you call the function, and not part of the function.

[t,y] = ode15s(@vdp1000,[0 3000],[2 0]);
plot(t,y(:,1),'-o')

function dydt = vdp1000(t,y)
%VDP1000  Evaluate the van der Pol ODEs for mu = 1000.
%
%   See also ODE15S, ODE23S, ODE23T, ODE23TB.

%   Jacek Kierzenka and Lawrence F. Shampine
%   Copyright 1984-2014 The MathWorks, Inc.

dydt = [y(2); 1000*(1-y(1)^2)*y(2)-y(1)];
end