Conditional variables with running ODE45

Question

Brilliant Purnawan 2020-11-19

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/653523-conditional-variables-with-running-ode45

回答： Alan Stevens 2020-11-19

Hi all, is it possible to call variables within an ODE45 and use if statements? So the general idea can be see in the code below, what I'm trying to do is that if the value of y(:,2) is greater than 0.3, than A will be 0.1 else, if its lower it will just run with a value of 0.1. Is this possible?

clear all, close all, clc
if y(:,2)>0.3
    A = 0.2;
else
    A = 0.1;
end
B = 0.1;
tspan = [0:4:200];
y0 = [0.95 0.05 0];
[t,y] = ode45(@(t,y)odefcn(y,A,B),tspan,y0);
figure(1)
hold on
plot(t,y(:,1),'-o')
plot(t,y(:,2),'-*')
plot(t,y(:,3),'-d')
function dydt = odefcn(y,A,B)
dydt = zeros(3,1);
dydt(1) = -A*y(2)*y(1);
dydt(2) = A*y(2)*y(1)-B*y(2);
dydt(3) = B*y(2);
end

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Alan Stevens 2020-11-19

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/653523-conditional-variables-with-running-ode45#answer_549783

在 MATLAB Online 中打开

Yes, but rearrange the coding as follows:

tspan = [0:4:200];
y0 = [0.95 0.05 0];
[t,y] = ode45(@(t,y)odefcn(t,y),tspan,y0);
figure(1)
hold on
plot(t,y(:,1),'-o')
plot(t,y(:,2),'-*')
plot(t,y(:,3),'-d')
function dydt = odefcn(~,y)
if y(2)>0.3
    A = 0.2;
else
    A = 0.1;
end
B = 0.1;
dydt = zeros(3,1);
dydt(1) = -A*y(2)*y(1);
dydt(2) = A*y(2)*y(1)-B*y(2);
dydt(3) = B*y(2);
end