the picture says it all.
i can't make sense of the variables controlling the field lines so cannot do it myself
[img]http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=539.0;attach=3468;image[/img]

when i can make sense of the codes, by observing the changes you made, i will learn more ;D
thanks!