LOGO-L> 3-d mesh & sombrero curve

[MHELHEFNY@FRCU.EUN.EG]

;Helo George Mills
;Here is the true "sombrero" surface as described in the old "matlab"
;manual; it is a surface that everybody likes to show.
;The surface has the simple equation z=sin(r)/r where r=sqrt(x^2+Y^2)
;for pupose of semilarity I used y=sin(r)/r where r=sqrt(x^2+z^2).
;this curve like the previous one of electric charges in space use the
;the mesh concept. of course many of the surfaces of revolution which
;was programed by rolling a curve thro' 360 degrees;could be drawn
;on a mesh.I shall try posting the code of one of these curves soon. 
;Hopping that you will enjoy it.
;Mhelhefni
;---------------------------------------------------------------
to go
turnon3d cs ;ht
make "step first questionbox [input step bet.(.5  - 2)][]
grid 14 :step
end

to grid :r :step
gridx :r :step gridz :r :step
end

to gridx :r :step
pu
for [x -:r :r :step][for [z -:r :r :step][make "xsq :x* :x make "zsq :z* :z
make "r sqrt(:xsq+ :zsq) +.001
make "f (sin :r*180/pi)/ :r 
setxyz :x*15 :f*200 :z*15] pu setz -zcor pd]
pu 
end

to gridz :r :step
pu
for [z -:r :r :step][for [x -:r :r :step][make "xsq :x* :x make "zsq :z* :z
make "r sqrt(:xsq+ :zsq) +.001
make "f (sin :r*180/pi)/ :r make "a 
setxyz :x*15 :f*200 :z*15] pu setx -xcor pd]
end

to turnon3d
; This is a library procedure for 3-d
perspective
setturtle -1
setxyz 800 1000 800
setturtle 0 
end
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