CODEWITHSUNDEEP
matlabodedifferential-equations
Anona anon
Anona anon

Reputation: 121

Not enough input arguments

I am trying to create an SIR Model (solving 3 differential equations with two parameters) and plot the solution for this on MATLAB and I keep getting the error 'Not enough input arguments'. I really can't see where I am going wrong. Here is the code:

function dx = sir(t,x) 
dx=[0; 0; 0]; 
beta = .003;
delta = 1;
dx(1)= -beta *x(1)*x(2); 
dx(2)=beta*x(1)*x(2)-delta*x(2); 
dx(3)=delta*x(2); 
%options = odeset('RelTol', 1e-4, 'NonNegative', [1 2 3]); 
[t,x] = ode45('sir', [0 10], [1000 1 0], options); 
plot(t,x); 
%legend('S', 'I', 'R'); 
end

Upvotes: 2

Views: 2033

Answers (1)

Doug Lipinski
Doug Lipinski

Reputation: 644

I think you have a serious misconception about how function calls and recursion work, or possibly you're just not familiar with programming. You need two separate things:

  1. Define a function and save it as sir.m. This defines your ODE. It should contain:
    function dx = sir(t,x) beta = .003; delta = 1; dx(1)= -beta *x(1)*x(2); dx(2)=beta*x(1)*x(2)-delta*x(2); dx(3)=delta*x(2);

  2. Run the code to solve your ODE. This can be directly pasted into the command window as long as sir.m is in your path or current directory:
    options = odeset('RelTol', 1e-4, 'NonNegative', [1 2 3]); [t,x] = ode45('sir', [0 10], [1000 1 0], options); plot(t,x); legend('S', 'I', 'R');

Note that step 1 defines the sir function and step 2 uses it. This needs to happen in two separate steps to prevent sir from calling itself (or more precisely in your case, calling a function, ode45, which calls sir again). This is called recursion and is not what you should be doing here.

Upvotes: 1

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