# How do I preallocate my variables for speed when creating an SIR model?

1 view (last 30 days)
Anika Ang on 19 Aug 2019
Hello. I am currently trying to graph an SIR model using matlab. I have a for loop in my code. My graph never seems to look right and I'm wondering if preallocating for speed might help. (Matlab also suggested this to me.)
My code is as follows:
for i=1:H
% Update time
t(i+1)=t(i)+h;
% Update S, I & R
k1S = fS(t(i) , S(i) , I(i) );
k1I = fI(t(i) , S(i) , I(i) );
k1R = fR(t(i) , I(i) );
k2S = fS(t(i)+h/2, S(i)+h/2*k1S, I(i)+h/2*k1I);
k2I = fI(t(i)+h/2, S(i)+h/2*k1S, I(i)+h/2*k1I);
k2R = fR(t(i)+h/2 , I(i)+h/2*k1I);
k3S = fS(t(i)+h/2, S(i)+h/2*k2S, I(i)+h/2*k2I);
k3I = fI(t(i)+h/2, S(i)+h/2*k2S, I(i)+h/2*k2I);
k3R = fR(t(i)+h/2 , I(i)+h/2*k2I);
k4S = fS(t(i)+h , S(i)+h *k3S, I(i)+h *k3I);
k4I = fI(t(i)+h , S(i)+h *k3S, I(i)+h *k3I);
k4R = fR(t(i)+h , I(i)+h *k3I);
S(i+1) = S(i) + h/6*(k1S + 2*k2S + 2*k3S + k4S);
I(i+1) = I(i) + h/6*(k1I + 2*k2I + 2*k3I + k4I);
R(i+1) = R(i) + h/6*(k1R + 2*k2R + 2*k3R + k4R);
end
I could really use some help in figuring out how to get my model to work. Thanks.