How to make ode15s not to cross zero?

6 Ansichten (letzte 30 Tage)
Akbar
Akbar am 6 Jul. 2018
Kommentiert: Steven Lord am 6 Jul. 2018
Here is the solution to a differential equation by simulink(ode15s, orange) and matlab(ode15s, blue). The solution mustn't cross Zero, how to prevent that in matlab ode15s?

Akzeptierte Antwort

Steven Lord
Steven Lord am 6 Jul. 2018
Does your problem involve a mass matrix? If not, use the NonNegative option as shown in the Knee Problem example on this documentation page.
If your problem does involve a mass matrix, use an Events function as shown in the bouncing ball example and the three body problem example on this documentation page. In this case you'll need to stop the solver, recompute what the new "initial" conditions should be, determine if the differential equations themselves change, and restart the solver. In the case of the bouncing ball, the ballode.m file recomputes the initial conditions at each bounce to reflect the ball rebounding from the floor.
  2 Kommentare
Akbar
Akbar am 6 Jul. 2018
Bearbeitet: Akbar am 6 Jul. 2018
Thank you for interesting solution. I am not using mass Matrix, and don't know if i Need it at all. I just know that the differential eq's is stiff, so i am using stiff solver, ode15s.
These are the Options i tries, and Matlab solution still crosses Zero. Seems like nonnegative thing didn't work. I wrote ones(1,14) because all 14 states should be nonnegative. I mean I have a 14 dimensional System.
options = odeset('RelTol',1e-6,'AbsTol',1e-6,'maxstep',0.2,'nonnegative',ones(1,14));
[t{ind},X{ind}] = ode15s(func,0:.01:170,X0,options);
Steven Lord
Steven Lord am 6 Jul. 2018
Specify 1:14 as the value for the NonNegative option.

Melden Sie sich an, um zu kommentieren.

Weitere Antworten (1)

Torsten
Torsten am 6 Jul. 2018
Tighten the tolerances RelTol and AbsTol, e.g.
opts = odeset('RelTol',1e-8,'AbsTol',1e-8);
Best wishes
Torsten.
  2 Kommentare
Akbar
Akbar am 6 Jul. 2018
That didn't help, I tried, thanks though.
Torsten
Torsten am 6 Jul. 2018
What is the differential equation ?

Melden Sie sich an, um zu kommentieren.

Kategorien

Mehr zu Programming finden Sie in Help Center und File Exchange

Produkte


Version

R2017b

Community Treasure Hunt

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

Start Hunting!

Translated by