When I do the following, the plot is doing something weird. It fills up a
triangle area between first and second points, after the axis command:
n = 5000.0
plot([n,-49.9,-49.9,-49.99,-50,-50])
axis([0,5,-50.1,-50+0.1])
This only happens at a very narrow window of boundary conditions.
If n is smaller (e.g. 4000) or if Y range is larger (e.g. set the min at -50.2
instead of -50.1), it becomes normal.
JC Hsu