Dear bosses, I ask, how to draw a semicircle in zedgraph? Y=root (r2 - (x - a) 2)

My idea is:

Dim x (99), y (99) as single 'set up 100 points
Dim as integer I
Dim x_start x_end, r as single 'x_start and x_end semicircle on the abscissa respectively two node
Dim step as single 'set x incremental
Dim as a single 'a centered on the horizontal axis of coordinates (a, 0)

R=(x_start - x_end)/2

Step=(x_end - x_start)/100

For I=0 to 99:
(I) + x=x_start + step
Y (I)=math.h SQRT (r ^ 2 - (x (I) - a) ^ 2)
Then put the x and y in pointpairlist
Next

But why semicircle always lack a piece at the end, you know why? Or what better alternatives?