Highlight a Section of a Plot

I would like to insert a vertical bar (light blue) from Time = 500 to Time = 650 to highlight that section of the curve. I believe patch is the tool to use. I followed examples provided on MathWorks, but my curve disappears when I use the recommended code. How can I incorporate patch into the code below?

plot(t,B);
xlabel('Time (in days)');
ylabel('Mosquitoes Searching for a Blood Meal');
h_xlabel = get(gca,'XLabel');
set(h_xlabel,'FontSize',14);
h_ylabel = get(gca,'YLabel');
set(h_ylabel,'FontSize',14);
set(gca,'fontName','Helvetica');
hold on;

I know that I should use patch before plotting my curve so that the vertical bar does not cover the curve.

Answer 1

[Star Strider]

Try this:

t = linspace(350, 750);                                             % Create Data
y = sin(2*pi*t/200 + 2) .* cos(2*pi*t/300)*0.2 + 0.2;               % Create Data

ptchidx = (t >= 500) & (t <= 650);                                  % Area To Shade

figure(1)
plot(t, y)
hold on
patch([t(ptchidx) fliplr(t(ptchidx))], [y(ptchidx) zeros(size(y(ptchidx)))], [0.6 0.4 0.9], 'FaceAlpha',0.3, 'EdgeColor','none')
hold off
grid

[árbol]

@Star Strider: Thanks for the suggestion! Using the code, I get this plot:

I would like the shaded region to stretch from y = 0 to y = .4. Would I modify the following line of code?

patch([t(ptchidx) fliplr(t(ptchidx))], [y(ptchidx) zeros(size(y(ptchidx)))], [0.6 0.4 0.9], 'FaceAlpha',0.3, 'EdgeColor','none')

Specifically, would I change this section?

[y(ptchidx) zeros(size(y(ptchidx)))]

Thanks!

[Star Strider]

My pleasiure!

If you just want the shaded box behind the plot, this works:

patch([500 650 650 500], [ 0 0 [1 1]*max(ylim)], [0.6 0.4 0.9], 'FaceAlpha',0.3, 'EdgeColor','none')

It is essentially the same code. The ‘x’-coordinates are now simply the limits of the box, and the ‘y’-coordinates go from 0 to the maximum value of the y-limits, so it will scale automatically if you change them.

If you want to hard-code the limits to 0.4, this will work:

patch([500 650 650 500], [ 0 0 [1 1]*0.4], [0.6 0.4 0.9], 'FaceAlpha',0.3, 'EdgeColor','none')

Experiment with the other properties of the patch function to get the result you want.

[árbol]

@Star Strider: Thank you!

[Star Strider]

As always, my pleasure!

[Luca Pozzi]

Thank you for the answer @Star Strider, it's very useful, but now here I come with a more complicated question: I would insert a vertical bar, just as the one @A. Kachalia succedeed to have, wherever the derivatives of the two signals in the plot haven't the same sign.

I thought to make a for (with some if inside) so to have in ptchidx all the intervals I'm looking for. Is it right? Is the rest of the code still valid for my purpose? Thank you very much

[Star Strider]

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