Adding a line to a plot without normalized coordinates

I am creating a scatter plot and I would like to add a line to the plot based on a y value. The y axis is not fixed and the line is specific to a value. How do I add a line to the plot?

example plot: scatter([0 10 20 30 40],[3 5 3 2 9]);

something like: line([0 40],[15 15], 'Color','r')

where line would go across the whole plot at 15 on the y and be red in color

Answer 1

[Sven]

You were so close:

figure
scatter([0 10 20 30 40],[3 5 3 2 9]);
hold on
plot([0 40],[15 15],'-', 'Color','r')

If you really wanted to use line(), you can do so, but you need to set its colour after it's been created:

figure
scatter([0 10 20 30 40],[3 5 3 2 9]);
hold on
h = line([0 40],[15 15])
set(h,'Color','r')

Answer 2

[Chmical]

Thanks alot Sven. worked great...