How do I plot a semicircle with lines at the maxima?

Going along an axis 'r' the bottom of a semicircle is plotted, how do I make the maximum points continue along parallel to the axis for a stated length?

Answer 1

[Paul Hill]

I ended up solving this problem myself, where 'z' is defined as the arc of a semicircle and 'h' being the height with which the arc was to stop and level out with lines;

depth = min(z)+ h;
z(z>(depth)) = (depth);
plot(z)

Answer 2

[Thorsten]

You can use

line

to draw a line.