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

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Elizabeth Pickford
Elizabeth Pickford 2024-4-25
编辑： Walter Roberson 2024-4-25
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);

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回答（1 个）

VBBV
VBBV 2024-4-25
编辑：VBBV 2024-4-25 
Q = [beta alpha lambda vac d gamma c m];

The size of the vector is 1x8

  2 个评论
VBBV
VBBV 2024-4-25
But you try to access the non existent element of vector in this line
B=Q(9)
Cris LaPierre
Cris LaPierre 2024-4-25
移动：Cris LaPierre 2024-4-25
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);

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