# File utilities/Flow.rb, line 71
  def Flow.holeField(x0,x1,f,m,y0)
    veloc = proc do |p|
      x = p[0]
      y = p[1]
      xf = 0
      yf = 0
      if (x<x0 || x>(2*x1 - x0))
        xf = f
      else
        sgny = (y-y0>0) ? 1 : -1
        absy = (y-y0) * sgny
        if (x< x1 && absy >  m*(x-x0))
            yf = m*f*sgny
            xf = f
        end
        if (x >= x1 && absy>=(2*x1-x0-x))
            yf = -m*f*sgny
            xf = f
        end
      end
      GeometricPoint.new([xf,yf])
    end
    return veloc
  end