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GRFAV

       SUBROUTINE  GRFAV (X1,X,X2, Y1,Y,Y2, N, PL2)
 C$    (Graph Average)
 C$    Plot a  graph by  connecting the  data points  by  straight
 C$    lines.  The points  defining the graph  are taken from  two
 C$    arrays, one holding the  X-values and the other  containing
 C$    the Y-values.  The respective  scales are indicated by  the
 C$    values  to  be  assigned  to  the  margins  of  the  graph.
 C$    Ordinarily  the  margins  would  be  given  rounded  values
 C$    slightly larger than the extreme data values.  However, the
 C$    graph may be centered in  various ways by assigning one  or
 C$    more margins considerably larger values.  Likewise excerpts
 C$    from the graph may be  chosen by giving the margins  lesser
 C$    values than the extremes.  The Y values themselves are  not
 C$    plotted,  but  instead  the   average  Y  defined  by   the
 C$    trapezoidal rule formula
 C$
 C$    AVY(K) = (1/2) SUM(I=2,K) (Y(I-1) + Y(I))/(K-1)
 C$
 C$    is graphed against X.  The arguments are:
 C$
 C$    X1.....X lower limit
 C$    X(N)...Array of X values (must be strictly increasing)
 C$    X2.....X upper limit
 C$    Y1.....Y lower limit
 C$    Y(N)...Array of Y values
 C$    Y2.....Y upper limit
 C$    N......Number of points
 C$    PL2....2-D pen movement subroutine, usually PL2CA
 C$    (31-JAN-82)