Problems replacing for-loops

1 次查看（过去 30 天）
Claudius Simon Appel
回答： David Hill 2021-4-21
Hello,
it has been a while since I needed to touch matlab seriously, or any programming language with heavy array-operation, for that matter.
We've been tasked to simplify and vectorise this function ('s for-loop). Aaaaand, I am stuck. Stuck trying to wrap my head around it, it just doesn't happen. This is supposed to be an introductory task, but this topic has always baffled my mind, and so far I didn't have the actual need to stop using for-loops. I know that you should not use them, but I was always having problems removing them. THey are the quick-and-dirty way to get stuff done, and my usual workloads are not big enough that I would care about saving the marginal amount of time I am saving each iteration.
Could someone give an explanation as to how this is supposed to be done?
Thank you.
Sincerely,
Claudius
clear all
close
clc
% set start param
S0=20;
I0=15;
R0=10;
a=3;
d=0.1;
lambda=0.3;
beta=0.1;
m=0.01;
alpha1=1;
alpha2=0.1;
r=0.2;
tmax=200;
SIR_01(S0,I0,R0,a,d,lambda,beta,m,alpha1, alpha2,r,tmax)
function SIR_01(S0,I0,R0,a,d,lambda,beta,m,alpha1, alpha2,r,tmax)
S=zeros(1,tmax);
I=zeros(1,tmax);
R=zeros(1,tmax);
S(1)=S0;
I(1)=I0;
R(1)=R0;
T(1)=0;
sMat=S
tMat=0:1:tmax
for t=1:1:tmax
T(t+1)=t;
S(t+1)=S(t)+(a-d*S(t)-(lambda*S(t)*I(t)/(1+alpha1*I(t)+ alpha2*I(t)^2))+beta*R(t));
I(t+1)=I(t)+((lambda*S(t)*I(t)/(1+alpha1*I(t)+alpha2*I(t)^2))-(d+m+r)*I(t));
R(t+1)=R(t)+(m*I(t)-(d+beta)*R(t)+r*I(t));
end
% plot(T,S,T,I,T,R); % deactivated the plot stuff to skip that while
% working. I am currently not interested in the plot itself.
IsequalNewT=isequal(T,tMat)
% title('SIR Model');
% legend('S(t)','I(t)','R(t)');
% xlabel('time, t');
% ylabel('Population');
end

请先登录，再回答此问题。

采纳的回答

David Hill
David Hill 2021-4-21
There is nothing wrong with for-loops. The only thing you can vectorize is T
T=0:tmax;
for t=1:1:tmax
S(t+1)=S(t)+(a-d*S(t)-(lambda*S(t)*I(t)/(1+alpha1*I(t)+ alpha2*I(t)^2))+beta*R(t));
I(t+1)=I(t)+((lambda*S(t)*I(t)/(1+alpha1*I(t)+alpha2*I(t)^2))-(d+m+r)*I(t));
R(t+1)=R(t)+(m*I(t)-(d+beta)*R(t)+r*I(t));
end

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Function Creation 的更多信息

标签

产品


版本

R2020b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by