Unable to resolve error using dde23

I am trying to solve a syste of delay differential equations, but the error: Derivative and history vectors have different lengths keeps occuring. I have taken notes from other similar questions and made sure that ylag and output of derivatives have the same length and made sure that my constants are not global. However, the error is not resolved.

For reference, this is my system:

Here is my code

lags=[2,2,2,2,2,2,2,2];
tspan=linspace(0,50);
sol=dde23(@deriv,lags,@history,tspan);
%-----------------------------------------
function dydt=deriv(~,y,z)
    ylag1=z(:,1);
    ylag2=z(:,2);
    ylag3=z(:,3);
    ylag4=z(:,4);
    ylag5=z(:,5);
    ylag6=z(:,6);
    ylag7=z(:,7);
    ylag8=z(:,8);
    n1=30290000;
    a1=0.98*n1;
    m=0.00055;
    eps=1/5;
    b1=0.000024246;
    chi=0.071;
    B1=0.5;
    eta=0.5;
    k1=0.185;
    phi1=0.26;
    alpha1=0.1155;
    delta=0.0225;
    omega1=0.26;
    dydt=[b1-((y(1)*B1*(y(3)+y(4)+(eta*y(6))))/a1)-b1*y(1)-m*ylag1;
        ((y(1)*B1*(y(3)+y(4)+(eta*y(6))))/a1)-(k1+eps)*y(2)-m*ylag2;
        k1*eps*y(2)-(alpha1+chi)*y(3)-m*ylag3;
        (1-k1)*eps*y(2)-(phi1+omega1)*y(4)-m*ylag4;
        k1*y(2)+alpha1*y(3)-chi*y(5);
        (phi1+omega1)*y(4)-(chi+delta)*y(6);
        ch*(y(5)+y(6))-b1*y(7)-m*ylag7;
        delta*y(5)];         
end
%-------------------------------------
function s=history(~)
    a1=0.98*30290000;
    s=[(a1-13),0,5,7,0,1,0,0];
end
%-------------------------------------

Answer 1

[Alan Stevens]

Change

    ylag1=z(:,1);
    ylag2=z(:,2);
    ylag3=z(:,3);
    ylag4=z(:,4);
    ylag5=z(:,5);
    ylag6=z(:,6);
    ylag7=z(:,7);
    ylag8=z(:,8);

to

    ylag1=z(1);
    ylag2=z(2);
    ylag3=z(3);
    ylag4=z(4);
    ylag5=z(5);
    ylag6=z(6);
    ylag7=z(7);
    ylag8=z(8);

and

ch*(y(5)+y(6))-b1*y(7)-m*ylag7;

to

chi*(y(5)+y(6))-b1*y(7)-m*ylag7;

and it works.

[SARAVANAKEERTHANA PERUMAL]

Thank you so much!