unset key
    set samples 3000
    set contour base
    set view map
    set nosurface
    set xrange [0:4]
    set yrange [0:2]

    set cntrparam level discrete 0.001,0.05

    set isosamples 100

    v(a) = 1 - 1/(2 * a)
    b(a, j) = (exp(-4 * a)/(4 * a**2) - (v(a))**2) - j/a
    c(a, j) = j / a * (exp(-2*a)/(2 * a) + v(a))**2

    msqrt(d) = exp({0.5,0}*log(d))
    max(x,y) = (x > y) ? x : y

    splot abs(imag(msqrt((-b(x, y) + msqrt(b(x, y)**2 - 4 * c(x, y)))/2)))