Don't understand the plot of x'=-a * x

Index
» Usage and Applications
» OpenModelica Usage and Applications
» Don't understand the plot of x'=-a * x

Page Start Prev 1 Next End

- Subscribe

Don't understand the plot of x'=-a * x

Don't understand the plot of x'=-a * x

Aug-09-15 23:32:12

Hi Guys,

I'm learning OpenModelica and I've already got stuck in the first example.

In the First Basic Class (HelloWorld) in OMNoteBook,
A class is defined like this:

Code:


class HelloWorld

  Real x(start = 1,fixed=true);

  parameter Real a = 1;

equation

  der(x) = - a * x;

end HelloWorld;

Then plot it

Code:


plot( x )

I was surprised about the plotted graph (BTW: how to insert local pictures to this post?)
-------------------------------
Firstly, I was expecting a linear graph like "y = -x"; Obviously I was wrong, but I don't know why.
Then I was trying to understand what is "time derivative". But still can not understand why the plotted graph started from "0, 1" and decrease as time increases.
Could you explain these basic concept for me? I searched for a while, but can not get it.