
plsvect: Set arrow style for vector plots 

DESCRIPTION:

    This function is used in example 22. 

SYNOPSIS:

plsvect(arrowx, arrowy, npts, fill)

ARGUMENTS:

    arrowx, arrowy (const PLFLT *,input) :    Pointers to a pair of arrays
    containing the x and y points which make up the arrow. The arrow
    is plotted by joining these points to form a polygon. The scaling
    assumes that the x and y points in the arrow lie in the range -0.5
    <= x,y <= 0.5. If both    arrowx and arrowy are NULL then the arrow
    style will be reset to its default. 

    npts (PLINT,input) :    Number of points in the arrays arrowx and
    arrowy. 

    fill (PLBOOL,input) :    If fill is true then the arrow is closed, if
    fill is false then the arrow is open. 
