Finding local minima for a signal

I have used the (findpeaks) function in Matlab in order to find the locations and the value of the peaks ( Local Maxima ) in the signal.

please, Is there any function to extract the local minimums of the following graph?

Answer 1

[Walter Roberson]

If you have a routine that can find local maxima, then to find local minima, apply the local maxima routine to the negative of the data. Like

      findpeaks(-X_Segments{nn},'MinPeakDistance', 20)

[neamah al-naffakh]

thank you so much mate

[Med Aymane Ahajjam]

Thanks!

Answer 2

[Azzi Abdelmalek]

Use

findpeaks(-your_signal)

[neamah al-naffakh]

thank you so much mate

[Med Aymane Ahajjam]

Thanks!

Answer 3

[Image Analyst]

You're probably okay with your data, but beware of findpeaks() if your max or min spikes have flat tops or bottoms. It will give only the first index. In that case you want to use the imregionalmin() function from the Image Processing Toolbox. Just look at this example with a min that has a flat bottom:

data = [ 1 3 4 2 2 2 4 4 5 6]  % Flat bottom with value of 2 from indexex 4-6
[peakValues, indexesOfPeaks] = findpeaks(-data)
peakValues = -peakValues
minIndexes = imregionalmin(data)

data =
     1     3     4     2     2     2     4     4     5     6
peakValues =
    -2
indexesOfPeaks =
     4
peakValues =
     2
minIndexes =
     1     0     0     1     1     1     0     0     0     0

[neamah al-naffakh]

hi mate, thanks for your effort i will check your solution and reply back , but do you mind have a look to this question please?

http://uk.mathworks.com/matlabcentral/answers/298931-calculating-the-mfcc-and-bfcc-for-a-signal

[Image Analyst]

I don't know how to answer that question.

Answer 4

[shima tavakoli]

my signal is asymmetric and its negative parts are different. how to deal with negative parts peaks then? cant negative the signal in this case!

[Image Analyst]

Who knows? You forgot to read this and forgot to attach your signal and a screenshot of it, so there's not much I can say, other than to write custom code to deal with it.