Problem with function envelope

Hi,

I have a problem with function envelope. It worked for all my set of data but, in one case, it didn't. When a function become constant, the envelope "goes away", creating a sort of asymptote. Or better, I think that it works, but when the function become constant I have to change stategy or stop the envelope.

I put there a right plot, without envelope, and the plot in which I get this problem.

I use this code, for example:

[low_dMRe, up_dMRe] = envelope(Int_dMRe_20,3000,'peak');

Could anyone help me, please?

Thank you in advance

Chiara

[Mathieu NOE]

hello Chiara

can you share some code + data ?

all the best

[Mathieu NOE]

hello again

maybe this FEX submission is worth a look / trial :

Envelope1.1 - File Exchange - MATLAB Central (mathworks.com)

[Chiara Gigoli]

Hi,

thank you very much for your answer.

Unfortunately, it doesn't work with my data...

But Star Strider gave me an helpful suggestion!

By the way, thank you a lot to give me this advice: it could be worth in other cases! :)

Chiara

Answer 1

[Star Strider]

The transition in the signal baselline is confusing envelope. It may be necessary to change the ‘np’ value, possibly to a lower number. I can reproduce the behaviour you’re seeing with different values, however with other values it comes close to behaving as expected. It will probably be necessary to just eliminate the envelope value above a specific time.

x = linspace(0, 10, 500);
y = exp(-1.25*x) .*  sin(2*pi*x*4.5) + (1-exp(-0.5*x));

[envhi,envlo] = envelope(y, 46, 'peak');

figure
plot(x, y)
hold on
patch([x flip(x)], [envhi flip(envlo)], 'g', 'FaceAlpha',0.5, 'EdgeColor','none')
hold off
grid
title('Original')
ylim([-1 1.5])

Lv = envlo < y;                             % Plot 'envelope' Only When 'envlo' Is Less Than The Signal

figure
plot(x, y)
hold on
% plot(x, envhi, '-r')
patch([x(Lv) flip(x(Lv))], [envhi(Lv) flip(envlo(Lv))], 'g', 'FaceAlpha',0.5, 'EdgeColor','none')
hold off
grid
title('Limited')
ylim([-1 1.5])

Something like this should also work for your signal.

.

[Chiara Gigoli]

Thank you a lot, it works!

That solve my question.

Chiara

[Chiara Gigoli]

Just one more question: I tried to plot the extreme value with a dashed line, but it doesn't work. I mean, the filling color and the envelope is right, but I can't plot the envelope boundary.

Could you give me some suggestion, please?

Chiara

[Star Strider]

As always, my pleasure!

If you are using code similar to what I posted, try this —

x = linspace(0, 10, 500);
y = exp(-1.25*x) .*  sin(2*pi*x*4.5) + (1-exp(-0.5*x));

[envhi,envlo] = envelope(y, 46, 'peak');

Lv = envlo < y;                             % Plot 'envelope' Only When 'envlo' Is Less Than The Signal

figure
plot(x, y)
hold on
% plot(x, envhi, '-r')
patch([x(Lv) flip(x(Lv))], [envhi(Lv) flip(envlo(Lv))], 'g', 'FaceAlpha',0.2, 'EdgeColor','none')
plot(x(Lv),envhi(Lv), '--g', 'LineWidth',1)
plot(x(Lv),envlo(Lv), '--g', 'LineWidth',1)
hold off
grid
title('Limited')
ylim([-1 1.5])

It is not easy to see the dashed green limit lines (use a version of the code you used to plot the original plot to plot them so they show up well), however they do exist and are plotted.

.

[Chiara Gigoli]

It perfectly worked!

Thank you so so much!

Chiara Gigoli

[Star Strider]

As always, my pleasure!