Re: Multiple variables in ode45

[Ron Crummett]

Vl is; well, it is my input signal. 

This differential euqation models a cruise controller where one vehicle 
gets its velocity based on the velocity of the vehicle in front of him.  
I am working on a fuzzy-logic based implementation for a class.  I have 
gotten the original linear controller to work using Simulink (the whole 
block design made it easy...) but I don't have fuzzy logic blocks to do 
the fuzzy controller and I would like to see if I could do the whole 
thing in Octave.  The solution to this equation is used in my fuzzy 
logic control system to determine an output that drives the automobile.

Anyway, to the actual question.  Vl is the velocity of the lead vehicle 
and I have defined it to start at 0, then climb to 13.4 (m/s, 30 mph) 
over 5 seconds, hold constant for 10 seconds, and then drop back to 0 
over 3 seconds.  So it is a piecewise-defined function, I guess that's 
the best way to put it.  I hope that helps, and thanks so much for the 
help given me.

-Ron

Shai Ayal wrote:

> I'm not sure I understand -- is Vl a function or constant?
> In general you e to solve your two equations (for u_dot and Vf_dot) 
> simultaneously, and ide45 should be able to do this.
>
> Shai
>
> Ron Crummett wrote:
>
> > Hi all -
> >
> > I am trying to solve a differential equation with ode45 that has two 
> > input variables and one output, but one of the input variables is 
> > dependent on the other.  When I try searching for anything like this 
> > it is to no avail (maybe I don't know what to search for).
> >
> > Anyway, the equation is
> >
> > u_dot = 0.5*e_dot+1.64*(e-1.14*Vf_dot)
> >
> > where e = Vf-Vl, Vl is my input, and Vf is my output.  The value of u 
> > is then fed into another system (which I do have the diff. eq. for) 
> > to get Vf, if that helps.
> >
> > Could someone give me some pointers on how to do this?  Thanks.
> >
> > -Ron
> >
> >
> >
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