# paste this code at the end of VectorFieldPlot 1.3
doc = FieldplotDocument('VFPt_anti-helmholtz_coil1', commons=True)
rx, ry = 1.0, 0.5
n=7
field = Field({'ringcurrents':[[0, -ry, pi/2, rx, -1], [0, ry, pi/2, rx, 1]]})

for sx, sy in [(a, b) for a in (-1, 1) for b in (-1, 1)]:
    for i in range(n):
        ex=1.30; t = (1 - (1 - 0.88 ** ex) ** ((i + 1.0) / n)) ** (1./ex)
        line = FieldLine(field, [sx*rx*t, sy*ry*t], directions='both', maxr=6)
        doc.draw_line(line, arrows_style={'dist':2.5, 'min_arrows':1})

doc.draw_currents(field)
doc.write()