How to Call a Function Within a Script?

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Learning
Learning 2022-11-21
回答： Cris LaPierre 2022-11-21
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')

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采纳的回答

Torsten
Torsten 2022-11-21
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')

更多回答（2 个）

David Hill
David Hill 2022-11-21
%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
Cris LaPierre
Cris LaPierre 2022-11-21
Ran in:
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

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