vertical lines in plot on left and right end

[dkrenn]

In the plot

plot(sin(3*pi*x)/sin(pi*x), (x,-5,5))

there are some artifacts at -5 and 5, namely a straight vertical line going to the top of the plot. They shouldn't be there. This also happens plotting the same function in the intervals (-9,9), (-10,10), (-15,15), (-17,17), (-18,18). In the plot

plot(sin(3*pi*x)/sin(pi*x), (x,-7,7))

something similar occurs, but the line goes down. This also happens for the interval (-14,14). For other interval boundaries than the mentioned (integers from -19 to 19) this does not happen. You can even mix, e.g. taking an interval (-7,5).

It also happens using functions sin(m*pi*x)/sin(pi*x) with m different from 3 (tested with 5).

Component: graphics

Keywords: plot boundary line

Issue created by migration from https://trac.sagemath.org/ticket/13754