matrix of functional data with functions in rows and measured times in columns;
or vector or functional observations, in this case id has to be specified
id
defaults to NULL for y matrix, is id-variables for y in long format
rug
logical. Should rugs be plotted? Defaults to TRUE.
All observations are marked by a small cross (pch=3).
Missing values are imputed by linear interpolation. Parts that are
interpolated are plotted by dotted lines, parts with non-missing values as solid lines.