Conditional variables with running ODE45
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Brilliant Purnawan
il 19 Nov 2020
Risposto: Alan Stevens
il 19 Nov 2020
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
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Alan Stevens
il 19 Nov 2020
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
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