Solving Second Order Differential Equations in Matlab

This video describes how to solve second order initial value problems in Matlab, using the ode45 routine. A full res version can be found at http://blanchard.ep.wisc.edu These videos were recorded for a course I teach as part of a distance masters degree. See http://mepp.engr.wisc.edu

Category:

Science & Technology

Tags:

• matlab
• numerical
• differential
• equation

[alpha001ful]

How can define " a function that defines the functions derived on previous slide (the first deivatives of Z and Y)". i think it is not shown here and that is my problem.

[jakeblanchard]

@alpha001ful

It is easiest if you send me a script I can debug. Send it to blanchard "at" engr.wisc.edu

Alternatively, download a sample script from

blanchard "dot" ep "dot" wisc "dot" edu/PublicMatlab/#IVP

[tomtomtramp]

I've been using your videos, thanks!. But, I think I'm writing the wrong code. I am developing a system to analysis the rocking motion of a block subjected to an earthquake excitation. The state vector is y(t)={theta(t) , theta'(t)}. and the Time-derivative vector f(t) is y'(t)= {theta'(t) , p^2(sin(alpha*sgn[theta(t)]-th­eta(t))+u''/g*cos(alpha*sgn[th­eta(t)]-theta(t))]}. I have the values for p, alpha, u'' and g. But I need theta(t), and theta'(t). Can anyone help, I really need it!

[jakeblanchard]

@tomtomtramp

You can email me at blanchard "at" engr.wisc.edu

[dequinox]

Thanks for this, I couldn't figure out why my code wasn't working...everything looked good. Then I realized I forgot to define g. Dang I want those two hours of my life back! Lol

[danielalonso23]

Thanks you very much dude¡¡¡¡¡¡, Greetings from Chile

[alpha001ful]

I tried to do the same simulation for a simple pendulum. Instead of y there , i had angle or variable called theta. Whenever i tried to run, Matlab always said "??? Input argument "theta" is undefined."........i have done exactly the same as here...

[jakeblanchard]

@pikachu832

Now for the second question. The differential equations are independent of the initial conditions. When Matlab solves the system, it starts with the initial conditions and then steps its way through time using the differential equations.