TITLE  'Two Point Charges'	
SELECT
	VectorGrid=50
DEFINITIONS                                     		
	Lx=1     Ly=1     r0=Ly/10
	q1=1      q2=1   d0=Ly/3      { Two charges separated by d0 }  	
	eps0=8.854e-12    c=1/(4*pi*eps0)
	Phi= q1*c/sqrt(x^2+(y+d0)^2)+ q2*c/sqrt(x^2+(y-d0)^2)    { Potential of two charges }
	E=-grad(Phi)   Em=magnitude(E)         { field calculation }             			
BOUNDARIES
   region 'domain'
	start(-Lx,-Ly)  line to (Lx,-Ly) to (Lx,Ly)  to (-Lx,Ly) to finish
	start(r0,d0) arc( center=0,d0) angle=360	{ Exclude circle of radius r0 around charge #2 }
	start(r0,-d0) arc( center=0,-d0) angle=360	{ Exclude circle of radius r0 around charge #1 }
PLOTS
	contour( Phi)      contour( Em) log      vector(E)
END