A numeric value, giving the aspect ratio for y axis to x-axis y/x for the 2D case,
it is redundant in the 3D case (default is NA),
see the official help for asp by typing "? asp".
xlab, ylab, zlab
Titles for the x and y axes in the 2D case, and x, y, and z axes in the 3D case,
respectively (default is "" for all).