MATLAB: DDE23 Function Error saying “The function has to be at the end. All the arguments after ‘sol’ have to be moved before the function”

dde23MATLAB

Hello,
I keep getting the error message that "The function has to be at the end. All the arguments after 'sol' have to be moved before the function" when I am using the DDE23 function
Below is my code. Could anyone please tell me what I am doing wrong?
Thank you!
 clear all
data=[0,1;
    13 5685;
    15 25796;
    18 110811;
    20 277178;
    22 384506;
    25 180901;
    27 193199;
    29 1242700;
    32 1470600;
    34 752500;
    36 121045];
%time data   
xdata = data(:,1);
%virus data
ydata = data(:,2);
%parameter guesses
param0 = [1000; 23; .1; 1e-6;];
%optimization algorithm
options = optimset('MaxFunEvals',2000);
param = fminsearch(@hiv_ssq, param0,[options]);
%solving the ode for the best fit
[t,yfit] = ode15s(@hiv_ode, xdata, [1e6;0;1], []);
%plotting V versus data
semilogy(xdata, ydata, 'ro', t, yfit(:,3), 'b');
 lags = [1]; % this is where we specify the vector of taus
 % we need a history function that is a column vector giving the value of y1
% and y2 in the past. Here we make these constant values.
     function x = history(t)
         x = [s/d; 0; 1];
     end
 % we define the function for the delay. the Y variable is the same as you
% should be used to from an ordinary differential equation. Z is the values
% of all the delayed variables.
    function  dYdt = ddefun(t,x,Z)
% additional variable
        y1 = x(1);
        y2 = x(2);
        y3 = x(3);
        % Z(:,1) = [y1(t - tau_1); y2(t - tau_2)]
       y3_tau1 = Z(3,1);
       dx(1) = (1e4)-.01*x(1)-b*x(1)*x(3);
       dx(2) = b*x(1)*x(3)-d2*x(2);
       dx(3) = N*d2*y_3tau1-c*x(3);
        dYdt = [dx(1); dx(2); dx(3)];
    end
 sol = dde23(@ddefun;lags;@history;tspan)
 y1 = sol.x(1,:); % note the y-solution is a row-wise matrix.
y2 = sol.x(2,:);
y3 = sol.x(3,:);

Best Answer

function dYdt = ddefun(t,x,Z) % additional variable y1 = x(1); y2 = x(2); y3 = x(3);
          % Z(:,1) = [y1(t - tau_1); y2(t - tau_2)]
         y3_tau1 = Z(3,1);
         dx(1) = (1e4)-.01*x(1)-b*x(1)*x(3);
         dx(2) = b*x(1)*x(3)-d2*x(2);
         dx(3) = N*d2*y_3tau1-c*x(3);
          dYdt = [dx(1); dx(2); dx(3)];
      end
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