MATLAB Central Newsreader - if there are more than one maxima and minima in a curve, how to identify them?

if there are more than one maxima and minima in a curve, how to identify them?

rakesh sepuri — Mon, 07 Jan 2008 16:34:01 -0500

Theres a curve which has many maximas and minimas. How to
identify each of these extreme points in the curve?
The curve is defined by integer datasets and is 2D.

Re: if there are more than one maxima and minima in a curve, how to identify them?

John Smith — Mon, 07 Jan 2008 17:54:02 -0500

"rakesh sepuri" <rakeshsepuri.nospam@mathworks.com> wrote in
message <fltk9p$p73$1@fred.mathworks.com>...
> Theres a curve which has many maximas and minimas. How to
> identify each of these extreme points in the curve?
> The curve is defined by integer datasets and is 2D.

Given a set of points, the convex hull of these points will
contain the extremum points. Finding convex hull is O(nlgn).

Re: if there are more than one maxima and minima in a curve, how to identify them?

ahmed — Tue, 17 Jun 2008 20:46:02 -0400

to john smith

if i have signal like this
a =
[0.0003,0.0103,0.0108,0.0113,0.0148,0.0188,0.0180,0.0186,0.
0195,0.0176,0.0189,0.0189,0.0198,0.0197,0.0204,0.0192,0.020
1,0.0193,

0.0184,0.0201,0.0212,0.0309,0.0442,0.0447,0.0479,0.0337,0.0
426,0.0500,0.0481,0.0488,0.0481,0.0491,0.0391,0.0479,0.0577
,0.0552,0.0563,0.0590,0.0622,0.0581,0.0610,0.0541,0.0293,0.
0307,0.0448,0.0519,0.0784,0.1600,0.1951,0.1914,0.2036,0.186
5,0.0719,0.0434,0.0543,0.0485,0.0435,0.0462,0.0506,0.0568,0
.0646,0.0687,0.0761,0.0788,0.0457,0.0417,0.0290,0.0326,0.07
11,0.0938,0.1112,0.0715,0.0526,0.0472,0.0437,0.0558,0.0627,
0.0639,.0717,0.0716,0.0738,0.0628,0.0495,0.0450,0.0361,0.03
40,0.0378,0.0372,0.0350,0.0364,0.0361,0.0403,0.0958,0.0861,
0.0308,0.0270,0.0320,0.0278,0.0271,0.0287,0.0254,0.0257,0.0
260,0.0270,0.0288,0.0283,0.0262,0.0257,0.0341,0.0449,0.0877
,0.0790,0.0112,0.0094,0.0094,0.0094,0.0074,0.0099,0.0108,0.
0099,0.0100,0.0094,0.0081,0.0081,0.0069,0.0067,0.0061,0.002
9]

you can plot it to see the shape: plot(a);

i like to take just into account the extreme points (peaks
and valleys) in this signal,
i dont like to consider ripples points in the signal

can i use convex hull to detect these points? if yes can
you explain in more detail

Re: if there are more than one maxima and minima in a curve, how to identify them?

Carlos Adrian Vargas Aguilera — Tue, 17 Jun 2008 21:52:02 -0400

Perhaps my functions extrema.m and extrema2.m help you. You
can find it at:

http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=12275&objectType=FILE

Best regards,

Carlos Vargas