Effacer les filtres
Effacer les filtres

ode45 goes busy endlessly when using the sign of a state variable

2 vues (au cours des 30 derniers jours)
Diaa
Diaa le 23 Avr 2021
Réponse apportée : Diaa le 23 Avr 2021
This term "- fr*Mass*9.8*sign(y(2))" makes ode45 busy forever specifically when using 'sign(y(2))'
I just need to make -fr*Mass*9.8=0 only when y(2)=0
Any explanations are highly welcomed.
clearvars
clc
close all
[t,y] = myexercise;
plot(t,y(:,2))
function [t,y] = myexercise
tspan = [0 , 10];
y0 = [ 0 ; 5 ];
Mass = 1300;
CD = 0.3;
fr = 0.015;
Af = 1.6;
traction = @(t) (t>3&t<5)*5*t;
[t,y] = ode45(@(t,y) deceleration(t,y) , tspan , y0);
function yp = deceleration(t,y)
yp = [ ...
y(2) ;...
( -0.5*1.23*CD*Af*y(2)^2 + traction(t) - fr*Mass*9.8*sign(y(2)) )/Mass ...
];
end
end
  2 commentaires
James Tursa
James Tursa le 23 Avr 2021
Please explain the physical problem and post the differential equation you are trying to solve so we can understand why you think you need the sign function.
Diaa
Diaa le 23 Avr 2021
It is a moving vehicle subjected to traction force and resistive aerodynamic drag and rolling resistance. Your comment made me realize that I forgot dividing the whole second equation by Mass. After fixing it, fr*Mass*9.8)*(y(2)>0) was enough to make it work.

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Réponse acceptée

Diaa
Diaa le 23 Avr 2021
Thanks to the explanation of Star Strider, the use of sign() can be replaced by fr*Mass*9.8)*(y(2)>0) to make it work.

Plus de réponses (1)

Walter Roberson
Walter Roberson le 23 Avr 2021
You really should read ballode to see how to use event functions. https://www.mathworks.com/help/matlab/math/ode-event-location.html

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