Clear Filters
Clear Filters

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

1 view (last 30 days)
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.
close all
[t,y] = myexercise;
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 ...
James Tursa
James Tursa on 23 Apr 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 on 23 Apr 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.

Sign in to comment.

Accepted Answer

Diaa on 23 Apr 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.

More Answers (1)

Walter Roberson
Walter Roberson on 23 Apr 2021
You really should read ballode to see how to use event functions.


Find more on Numerical Integration and Differential Equations in Help Center and File Exchange


Community Treasure Hunt

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

Start Hunting!