Advanced Programming Guide

6.5 Programming with the plottools Package • 247–4–3–2–1012–3 –2 –1y 01 2 3321–3–2–10 xSummary• The first section of the dropshadow procedure determines if you havespecified a contours option in the optional arguments (those afterthe fourth argument), making use of the hasoption procedure.• The next section of dropshadowplot determines the z value of thebase. Note that you must specify ranges differently for formula thanfor function input.• The remaining sections create the correct plotting objects which representthe two types of contour plots.The dropshadowplot procedure embeds the two-dimensional contourplot into three-dimensional space using the transformation(x, y) ↦→ [x, y, minz]from R 2 → R 3 . Finally, it displays the two plots in one three-dimensionalplotting object.Note: You can provide an alternate number of levels or specify the precisecontour locations via the contours option. Thus,> dropshadowplot( expr, x=-3..3, y=-3..3, z=-4..3,> filled=true, contours=[-2,-1,0,1,2] );