Construction of Drop Lines in Plot

Hi All

    > I am new to Matplotlib, and was wondering if anybody knew
    > of an easy way to construct a dropline from a data point in
    > a plot to the x axis, i.e. a vertical line from (x1,y1) to
    > (x1,0)?

  ax.plot((x1, x1), (y1, 0), linestyle='-', color='black', linewidth=2)

should do it... There are some helper functions vline and
axvline you may want to look at

The first will draw a vertical line that spans the axes vertical
extent regardless of zoom level, and the second simply draws a
vertical line at a given x from y1 to y2. vline supports many
vertical lines and for a single one as in your example, it's easy
enough to just use plot.