code: func (g GridType) Plot(pdf *Fpdf, xMin, xMax float64, count int, fnc func(x float64) (y float64)) {
  	if count > 0 {
  		var x, delta, drawX0, drawY0, drawX1, drawY1 float64
  		delta = (xMax - xMin) / float64(count)
  		x = xMin
  		for j := 0; j <= count; j++ {
  			if j == 0 {
  				drawX1 = g.X(x)
  				drawY1 = g.Y(fnc(x))
  			} else {
  				pdf.Line(drawX0, drawY0, drawX1, drawY1)
  			}
  			x += delta
  			drawX0 = drawX1
  			drawY0 = drawY1
  			drawX1 = g.X(x)
  			drawY1 = g.Y(fnc(x))
  		}
  	}
  }
docs: // Plot plots a series of count line segments from xMin to xMax. It repeatedly
  // calls fnc(x) to retrieve the y value associate with x. The currently
  // selected line drawing attributes are used.