# set terminal pngcairo  background "#ffffff" enhanced font "arial,10" fontscale 1.0 size 600, 400 
# set output 'vector.1.png'
set label 1 "-q" at -1, 0, 0 centre norotate back nopoint offset character 0, 0, 0
set label 2 "+q" at 1, 0, 0 centre norotate back nopoint offset character 0, 0, 0
set view map
set isosamples 31, 31
unset surface 
set contour base
set cntrparam levels discrete -3,-2 ,-1 ,-0.5 ,-0.2 ,-0.1 ,-0.05 ,-0.02 ,0 ,0.02 ,0.05 ,0.1 ,0.2 ,0.5 ,1 ,2 ,3 
set rrange [ 0.00000 : 10.0000 ] noreverse nowriteback
set trange [ -5.00000 : 5.00000 ] noreverse nowriteback
set urange [ -5.00000 : 5.00000 ] noreverse nowriteback
set vrange [ -5.00000 : 5.00000 ] noreverse nowriteback
set xrange [ -10.0000 : 10.0000 ] noreverse nowriteback
set x2range [ -10.0000 : 10.0000 ] noreverse nowriteback
set yrange [ -10.0000 : 10.0000 ] noreverse nowriteback
set y2range [ -10.0000 : 10.0000 ] noreverse nowriteback
set zrange [ -10.0000 : 10.0000 ] noreverse nowriteback
set cbrange [ -10.0000 : 10.0000 ] noreverse nowriteback
r(x,y)=sqrt(x*x+y*y)
v1(x,y)=  q1/(r((x-x0),y))
v2(x,y)=  q2/(r((x+x0),y))
vtot(x,y)=v1(x,y)+v2(x,y)
e1x(x,y)= q1*(x-x0)/r(x-x0,y)**3
e1y(x,y)= q1*(y)/r(x-x0,y)**3
e2x(x,y)= q2*(x+x0)/r(x+x0,y)**3
e2y(x,y)= q2*(y)/r(x+x0,y)**3
etotx(x,y)=e1x(x,y)+e2x(x,y)
etoty(x,y)=e1y(x,y)+e2y(x,y)
enorm(x,y)=sqrt(etotx(x,y)*etotx(x,y)+etoty(x,y)*etoty(x,y))
dx1(x,y)=coef*etotx(x,y)/enorm(x,y)
dy1(x,y)=coef*etoty(x,y)/enorm(x,y)
dx2(x,y)=coef*etotx(x,y)
dy2(x,y)=coef*etoty(x,y)
GPFUN_r = "r(x,y)=sqrt(x*x+y*y)"
q1 = 1
x0 = 1.0
GPFUN_v1 = "v1(x,y)=  q1/(r((x-x0),y))"
q2 = -1
GPFUN_v2 = "v2(x,y)=  q2/(r((x+x0),y))"
GPFUN_vtot = "vtot(x,y)=v1(x,y)+v2(x,y)"
GPFUN_e1x = "e1x(x,y)= q1*(x-x0)/r(x-x0,y)**3"
GPFUN_e1y = "e1y(x,y)= q1*(y)/r(x-x0,y)**3"
GPFUN_e2x = "e2x(x,y)= q2*(x+x0)/r(x+x0,y)**3"
GPFUN_e2y = "e2y(x,y)= q2*(y)/r(x+x0,y)**3"
GPFUN_etotx = "etotx(x,y)=e1x(x,y)+e2x(x,y)"
GPFUN_etoty = "etoty(x,y)=e1y(x,y)+e2y(x,y)"
GPFUN_enorm = "enorm(x,y)=sqrt(etotx(x,y)*etotx(x,y)+etoty(x,y)*etoty(x,y))"
coef = 0.7
GPFUN_dx1 = "dx1(x,y)=coef*etotx(x,y)/enorm(x,y)"
GPFUN_dy1 = "dy1(x,y)=coef*etoty(x,y)/enorm(x,y)"
GPFUN_dx2 = "dx2(x,y)=coef*etotx(x,y)"
GPFUN_dy2 = "dy2(x,y)=coef*etoty(x,y)"
xmin = -10.0
xmax = 10.0
ymin = -10.0
ymax = 10.0
splot vtot(x,y) w l