;David Parker "2D Flow" example of Steiner net flow
;annotated and modified by gkf for UIUC Math 303 23apr03
a := 1.5                    ;separation of the poles
a.minimum := 0               
a.maximum := 3
b := 1                      ;flow speed
b.minimum := .1 
b.maximum := 2 
c := 2                      ;sine wave frequency
c.minimum := -4 
c.maximum := 4 
d := 4                      ;sine wave frequency
d.minimum := -8
d.maximum :=  8
graph3d.box := true
graph3d.mesh := true
graph3d.view := top
graph3d.perspective := false
graph3d.resolution := 101
graph3d.highlight := 0
graph3d.shading := 0
graph3d.contrast := 1/2
graph3d.transparency := 0
graph3d.color := byheight
graph3d.background := white
graph3d.minimumx := -4
graph3d.maximumx := 4
graph3d.minimumy := -3
graph3d.maximumy := 3
graph3d.minimumz := -0.0001
graph3d.maximumz := 0.0001
graph3d(( 
  sin( 
     c*pi*(angle(x+a,y)-angle(x-a,y)) 
  )=0
, sin( 
     d*pi*ln(sqrt(((x+a)^2+y^2)/((x-a)^2+y^2))) 
     + b*time            
  )=0
))