algorithm of envelope function 'peak' option

Hello,

I'm using the envelope function with 'peak' option, [yupper,ylower] = envelope(x,np,'peak').

The description says, 'The envelopes are determined using spline interpolation over local maxima separated by at least np samples.'

I'm wondering that what order is used in the spline interpolation and also how the local maxima are calculated, separated by 'at least' np samples.

If I can, I would like to know the algorithm too.

Thank you.

Answer 1

[Walter Roberson]

The local maxima are found using findpeaks() with the 'MinPeakDistance' option

spline interpolation is done using interp1() with the 'spline' option. interp1 defines

"Requires at least 4 points, falling back to linear or quadratic interpolation if 2 or 3 points are supplied, respectively" which implies that it is normally cubic spline.

[준영]

Thank you for your reply.

I have one more question.

Where can we find such used codes if we want to know how the matlab function works?

Thank you very much.

[Walter Roberson]

Sometimes you can just (for example)

edit envelope

It happens that source code for envelope is available.

Sometimes you need to use something like

which envelope(1:10, 2, 'peak')

in order to find out which specific method is being selected when envelope(1:10, 2, 'peak') is being called. After you which() has produced an answer, you can edit the method indicated.

But sometimes you encounter situations such as

which dictionary

that will reply back

dictionary is a built-in method % dictionary constructor

and if you encounter such a situation, you will be unable to view the source code, as it is written in C++ or C or FORTRAN and is not available.

Occasionally you will encounter code being implemented in .p files. There is (deliberately) no documented method of viewing .p files.