Your function requires additional parameters. One way to pass them is to use an anonymous function as extra layer
% params
N = 2; % two oscillators: melatonin and cortisol
omega = 2*pi; % intrinsic frequency of both oscillators: 24 hours
tau = 5*pi/9; % time delay: 3 hours and 20 minutes
h = 0.1; % step size
iter = 500; % number of iterations
tspan = 0:h:h*iter; % time
K = [0 0.5; 0.5 0]; % initialising the coupling matrix
% extra layer function so that omega and K are available to ddefun
myfun = @(t,theta,Z)ddefun(t,theta,Z,omega,K);
% call to solver
sol = dde23(myfun,tau,@history,tspan);
% Subfunctions
function dthetadt = ddefun(t,theta,Z,omega,K)
thetalag1 = Z(:,1);
dthetadt = [omega+K(1,2)*sin(theta(2)-theta(1));
omega+K(2,1)*sin(thetalag1(1)-theta(2))];
end
function s = history(t)
s = ones(2,1);
end
You can find other strategies to pass extra parameters here
