Index exceeds number of array elements. Index must not exceed 8. HELP

Here's my model code:

clear all;
close all;
S = 99;
I = 1;
R = 0;
N = 100; %Total population
beta= 0.1; % birth rate
alpha= 0.1; % infection person to person rate
lambda= 0.3; % infection by water rate
vac= 0.05; % recovery by vaccination rate
d= 0.03; % death rate
gamma= 0.8; % recovery rate
c= 0.9; % rate of contamination
m= 0.4; % rate of decay of V. cholera
t_f = 500; %Ending time of simulation
Q = [beta alpha lambda vac d gamma c m];
[t,y]=ode45('cholera_de',[0:t_f/100:t_f],[S I R]',[],Q);
figure(1)
plot(t,y(:,1),'k-',t,y(:,2),'r--',t,y(:,3),'b:');
xlabel('\bf Time (days)');
ylabel('\bf Number of People by Category');
legend('S','I','R');
z=y(end,:)'
SN=y(:,1)/N;
IN=y(:,2)/N;
figure(2)
plot(IN,SN);
xlabel('\bf I/N');
ylabel('\bf S/N');
r0=beta/beta
[maxIN,y_maxtime]=max(y(:,2)/N);
maxIN
maxtime=y(y_maxtime)
eqIN=y(100,2)/N;
eqIN

And my Function code:

function dy=cholera_de(t,Y,flag,Q)
beta= Q(1);
alpha= Q(2);
lambda= Q(3);
vac= Q(4);
d=Q(5);
gamma=Q(6);
c=Q(7);
m=Q(8);
B= Q(9);
S= Y(1);
I= Y(2);
R= Y(3);
N= S+I+R;
dy(1,1)= beta - alpha*I - lambda*B - vac*S - d;
dy(2,1)= alpha*I + lambda*B - d - gamma*I;
dy(3,1)= gamma*I + vac*S - d;
dy(4,1)= c*I - m*B;

Why am I getting this error?

Index exceeds the number of array elements. Index must not exceed 8.

Error in cholera_de (line 11)

B= Q(9);

Error in odearguments (line 92)

f0 = ode(t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 104)

odearguments(odeIsFuncHandle,odeTreatAsMFile, solver_name, ode, tspan, y0, options, varargin);

Error in cholera_model (line 22)

[t,y]=ode45('cholera_de',[0:t_f/100:t_f],[S I R]',[],Q);

Answer 1

[VBBV]

Q = [beta alpha lambda vac d gamma c m];

The size of the vector is 1x8

[VBBV]

But you try to access the non existent element of vector in this line

B=Q(9)

[Cris LaPierre]

The error means you are trying to access an element in Q that does not exist. From the message, Q contains 8 elements, so you get an error when trying to indext a 9th element.

This makes sense. You define Q as having 8 elements.

Q = [beta alpha lambda vac d gamma c m];

but in your function, you try to access a 9th element

B= Q(9);