Hi Prof.Hwang

the mathematical model is a spring mass system with air resistance.

Lucky for the EJS manual from Prof. Paco, the evolution equation are given.

The complexity arises due to my attempt

1. to make it into a applet where users can conduct their own experiment
2. instructional design more friendly ( text etc)
3. greater control to study certain quantities alone or together ( checkbox etc)
4. my lack of knowledge in javascripts (i am learning by refering to examples for syntax and logic)
5. use of the fields to debug and make sense what they mean in xml codes

which is why i don't get what xsp and ysp do  ??? it is because i use the wrong field (old) 1.0 type ?

maybe i try to change to 2.0 type of field  :D

Thanks to you and prof. paco, the learning journey is tough but i hope to be good enough some day.

Anyway, back to the xml file, i think the polygon is not what i wanted because the user need

To get one plot point:

1. wait for oscillation to be "steady";
2. change Xmax to zero;
3. wait for Xmax to become highest or steady;
4. pause simulation;
5. click on button to store Xmodplot = Xmax;
6. change frequency to another value
7. set Xo = 1 m again
8. click play

All these just to get one point to plot .

To get another data point:

repeat 1 to 8

Question of Choice of Polygon.
Is it better to be particleset ? i was thinking to show big dots (user has to conclude on their own) rather than a line which the user can conduct very few data points or in not increasing order of frequency.

I try to work on it at home later.

Thanks for help  :)