LOGO-L> 3-d mesh of electric field

[MHELHEFNY@FRCU.EUN.EG]

;Helo George Mills
;Here is the code to show electric field due to two opposite charges
;drawn on a 3-D space grid.
;this same grid used to be done by famous packages like "Matlab".
;The electic field intensity is first treated by stepping in the x 
;direction, then it is stepped in the z direction, while the y-axis
;is the one to be calculated;teatchers may use this model in physics
;lessons.
;Hoping that some body will develop the code to draw the contour map 
;(equipotential lines) of the field.
;hint:- the contour map could be drawn without using 3-d extensions
;setting different turtles with their own colours for each line hight.
;Enjoy it
;Best Regards
;Mhelhefni
;------------------------------------------------------------------ 
to go
turnon3d cs ht
make "step first questionbox [input step bet.(.08 for details - 1 for speed)][]
ifelse :step <.16 [gridx .3 -.4 :step rt 90 label[contour_lines_apear]]~
[grid .3 -.4 :step rt 90 label[two_opposite_elect_charges]]
end

to grid :q :q1 :step
gridx :q :q1 :step gridz :q :q1 :step
end

to gridx :q :q1 :step
for [x 0 14 :step][for [z 0 14 :step][make "xsq (:x- 11)*(:x- 11) make "zsq
(:z- 9)*(:z- 9)
make "xsq1 (:x- 4)*(:x- 4) make "zsq1 (:z- 7)*(:z- 7)
make "f :q/(:xsq+ :zsq+ .05)
make "f1 :q1/(:xsq1+ :zsq1+ .05)
pd setxyz :x*30 (:f+ :f1)*60 :z*30]pu home]
end

to gridz :q :q1 :step
for [z 0 14 :step][for [x 0 14 :step][make "xsq (:x- 11)*(:x- 11) make "zsq
(:z- 9)*(:z- 9)
make "xsq1 (:x- 4)*(:x- 4) make "zsq1 (:z- 7)*(:z- 7)
make "f :q/(:xsq+ :zsq+ .05)
make "f1 :q1/(:xsq1+ :zsq1+ .05)
pd setxyz :x*30 (:f+ :f1)*30 :z*30]pu home]
end

to turnon3d
; This is a library procedure for 3-d
perspective
setturtle -1
setxyz 1000 1000 1000
setturtle 0 
end
;----------------------------------------------------------------------
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