Usage: function: one or more functions exploded by ;
		   w width (300)
		   h heigth (300)
		   x_min= min value of x (-1)
		   x_max= max value of x (1)
		   text= A text
		   text_x=x coordinate of text (0).
		   text_y=y coordinate of text (0).
		   x1,y1 = coordinate for a point representation
		   x2,y2 = Values for a second point representation