Error using dde23 (line 224) Derivative and history vectors have different lengths - dde

Question

I am trying to solve a couple system of delay differential equations using dde23. While running the following code, I am getting an annoying error "Derivative and history vectors have different lengths"
function sol = prob1
clf
global Lembda alpha u1 u2 p q c d k a T b zeta1 zeta2 A1 A2
Lembda=2; b=0.07; d=0.0123; a=0.6; k=50; q=13; c=40; p=30; alpha = 0.4476; T=1; B=0.4; A1 =200; A2=100; zeta1=10; zeta2=30;
lags = [ 10; 0.2; 2; 10; 0.2; 10; 0.2; 2; 10; 0.2; 15; 0.9; 0.17; 0.01; 0.5; 0.000010; 0.00002];
sol = dde23(#prob2f,T,lags,[0,10], u1, u2);
function yp = prob2f(t,y,Z,B)
global Lembda alpha p b d c q T a k zeta1 zeta2 A1 A2
x2 = y(1);
y2 = y(2);
z2 = y(3);
v = y(4);
w = y(5);
xlag = Z(1,1);
vlag = Z(2,1);
%%%%%%%%%%%%%%%%
x1 = y(6);
y1 = y(7);
z1 = y(8);
v1 = y(9);
w1 = y(10);
x1lag = Z(1,1);
v1lag = Z(2,1);
%%%%%%%%%%%%%%%%%%%
lambda1 = y(11);
lambda2 = y(12);
lambda3 = y(13);
lambda4 = y(14);
lambda5 = y(15);
u1 = y(16);
u2= y(17);
lambda1lag = Z(1,1);
lambda4lag = Z(2,1);
%%%%%%%%%
dxdt=Lembda-d*x2-B*x2*v;
dydt=B*exp(-a*T)*xlag*vlag-a*y2 - alpha*y2*w;
dzdt=alpha*y2*w - b*z2;
dvdt=k*y2-p*v;
dwdt=c*z2-q*w;
%%%%%%%%%
dx1dt=Lembda-d*x1-(1-u1)*B*x1*v1;
dy1dt=(1-u1)*B*exp(-a*T)*x1lag*v1lag-a*y1 - alpha*y1*w1;
dz1dt=alpha*y1*w1 - b*z1;
dv1dt=(1-u2)*k*y1-p*v1;
dw1dt=c*z1-q*w1;
%%%%%%%%%%
dlambda1dt= A1+lambda1*d+(1-u1)*lambda1*B*v1-(1-u1)*lambda2*B*v1lag*exp(-a*T)*lambda2*(T);
dlambda2dt= a*lambda2+(lambda2-lambda3)*alpha*w1-lambda4*k*(u2-1);
dlambda3dt= b*lambda3-c*lambda5;
dlambda4dt= A2+(1-u1)*lambda1*B*x1+lambda4*p+lambda4*(T)*lambda2*x1lag*(u2-1)*exp(-a*T);
dlambda5dt=alpha*lambda2*z1-alpha*lambda3*z1+lambda5*q;
du1dt = ( lambda2*x1lag*v1lag - lambda1*x1*v1)*(B/zeta1);
du2dt =(lambda4*k*y2)/zeta2;
yp = [ dxdt; dydt; dzdt; dvdt;dwdt; dx1dt; dy1dt; dz1dt; dv1dt;dw1dt; dlambda1dt; dlambda2dt; dlambda3dt ;dlambda4dt ;dlambda5dt; du1dt; du2dt ];
Can anyone guide me, to be able to resolve this issue?
Thanks

Answer 1

The error occurs because your return vector yp is not the same size as the lags vector.
The lags vector has length 17, but the yp vector comes out to be of length 10. Even though you have 17 entries in yp, many of them as []
yp = [ dxdt; dydt; dzdt; dvdt;dwdt; dx1dt; dy1dt; dz1dt; dv1dt;dw1dt;
dlambda1dt; dlambda2dt; dlambda3dt ;dlambda4dt ;dlambda5dt; du1dt; du2dt ];
K>> dxdt
dxdt =
[]
K>> length(yp)
10
lags = [ 10; 0.2; 2; 10; 0.2; 10; 0.2; 2; 10; 0.2; 15; 0.9; 0.17; 0.01;
0.5; 0.000010; 0.00002];
sol = dde23(#prob2f,T,lags,[0,10], u1, u2);
K>> length(lags)
17
The return from your prob2f() should have same length as lags. This is why the error shows up
f0 = feval(ddefun,t0,y0,Z0,varargin{:});
nfevals = nfevals + 1;
[m,n] = size(f0);
if n > 1
error(message('MATLAB:dde23:DDEOutputNotCol'))
elseif m ~= neq
error(message('MATLAB:dde23:DDELengthMismatchHistory')); <========
end
You need to check your prob2f function and make sure yp has same length as lags.