Plot dashed lines to given y value on a graph

How can I get dashed lines from each axis out to a point at a graph, given by a specified y value?

Somehow i would also like to get the corresponding x value represented.

Thanks for any help. For use in an example:

x = [0:1:25];

y = x * pi ;

plot(x,y)

Answer 1

[Walter Roberson]

x = [0:1:25];
y = x * pi ;
stem(x,y, '--')

[Walter Roberson]

Somehow i would also like to get the corresponding x value represented.

annotation() maybe? text() maybe?

[Rudolf]

Stem is only plotting the graph sort of. I was looking for a way to get one dashed line from y-axis, for example at value 30, to go out to where it hits the graph, then a dashed line from this point down to the x-axis. And then in some way represent that x-value. I will check out text(), thanks.

[Walter Roberson]

x = [0:1:25];
y = x * pi ;
plot(x, y);
hold on
ytarg = 30;
[~,yidx] = min(abs(y-ytarg));
xtarg = x(yidx);
plot([0, xtarg xtarg], [30 30 0], '--');
text(2, 50, sprintf('x=%g', xtarg), 'HorizontalAlignment', 'center')
plot([2 xtarg], [50 y(yidx)], '-k');
hold off

With this code, you would need to use a finer-grain x to have the points match up better.

You could interpolate to find a more accurate x, but the ease of doing that would depend upon whether the y is monotonic. y is monotonic in this case, so it could be done easily with xi = interp1(y,x,30)

[Rudolf]

Perfect!! Thank you so much! This solved the challenge.