MATLAB: Not enough input arguments ode45

error ode45not enough input arguements

Hi all, I have been trying to understand the use of ode solvers in MATLAB. In the process, I started with first order equations and all went well. The moment I started trying out second order systems, the trouble started. When I run the code, it shows 'not enough input arguments'. I thought that it may the problem with my code and then I started trying codes given as example in text books (Otto&Denier etc.). For every code, every time I run, the same issue pops up. And the code seems to be correct. Please help me to sort it out. I have attached the screenshot of the error message.
">> lorenz Error using lorenz (line 5) Not enough input arguments." This was a code I chose from a text book.
    if true
      % code
function dx=lorenz(t,x)
sigma=10;
rho=28;
beta=8/3;
dx=[sigma*(x(2)-x(1));x(1)*(rho-x(3)-x(2));x(1)*x(2)-beta*x(3)];
x0=[0 1 1.05];
tspan=[0,20];
[t,x]=ode45(@lorenz,tspan,x0);
plot(x(:,1),x(:,3))
    end

Best Answer

Separate the funciton from the rest
function dx=lorenz(t,x)
  sigma=10;
  rho=28;
  beta=8/3;
  dx=[sigma*(x(2)-x(1));x(1)*(rho-x(3)-x(2));x(1)*x(2)-beta*x(3)];
end
and invoke ode45 correctly
x0=[0 1 1.05];
tspan=[0,20];
[t,x]=ode45(@(t,x) lorenz(t,x),tspan,x0);
plot(x(:,1),x(:,3))
Does it work now?
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