as this is listed as a doc issue, I pushed a change to the plot docstring that describes the current behavior of a scalar+vector combination as a series of points.

https://hg.savannah.gnu.org/hgweb/octave/rev/8b17f4ebc13f

if that's all that's required we can probably close the report. But as rik pointed out, and I just verified with v 2023b, matlab produces the same output but with marker set to 'none'.

is that something we care to emulate?

Plotting

x=(1:10)';
y=1;
plot(x,y)

gives ten points of different colour. I would have expected the y to be singleton-expanded and thus a single line to be plotted. The point is that if x is a very large vector, the execution takes unexpectedly long, while a single line would have been drawn much quicker. I see that the Matlab documentation says that in the present case discrete points are plotted, but they say nothing about whether they should have the same style or not (which probably would also complete faster than the present case). As I see it, the octave documentation does not treat the present case at all.

So this is at least a documentation bug. Perhaps it is also a Matlab incompatibility, if Matlab should have the same style on all points. What I do not get is their point that to see the points a marker symbol has to be specified -- if no symbol is specified, does the plot stay empty? Because in fact that is what happens if in octave I execute plot(x,y,'-'), presumably because it plots ten lines consisting only of a single point. Thus, for the simplest conceivable plot you can request, just a single horizontal line, you have to do something like

plot([0 1],[1 1])

while the more obvious and simple

plot([0 1],1)

does not work, not even with an '-'. That's why I would argue here even for a voluntary Matlab incompatibility.