draw a polyline or a polygon
xpoly(xv,yv [,dtype [,close]])
matrices of the same size (points of the polyline).
string (drawing style). default value is "lines".
integer. If close=1, the polyline is closed; default value is 0.
xpoly draws a single polyline described by the vectors of
yv are matrices they are considered as vectors by
concatenating their columns.
dtype can be
"lines" for using the current line style or
"marks" for using the current mark to draw the polyline.