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Finding local minimums/maximums for a set of data
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Hi, I have a set of data which oscillates between minimums and maximum values. The min and max values change slightly over time. I want to see the trend of changing of min and max values over time. In order to do that, it seems that I need to extract the local min and local maximums.
Is there any function to extract the local minimums and maximums of the following graph?
Thanks.
![](https://www.mathworks.com/matlabcentral/images/broken_image.png)
댓글 수: 4
Steev Mathew
2021년 3월 4일
Thanks! This helped me a lot. I was looking for a way to filter out noise from my data.
Anupama V
2022년 11월 6일
How to find the valley of a ppg signal?(secondary peak of a signal)
채택된 답변
Star Strider
2012년 7월 22일
편집: Star Strider
2012년 7월 22일
Another option is ‘findpeaks’ in the Signal Processing Toolbox. It will give you the maximum (and indirectly the minimum) values and their index locations. If ‘Data’ is the vector that produced the plot, to find the maxima and minima:
[Maxima,MaxIdx] = findpeaks(Data);
DataInv = 1.01*max(Data) - Data;
[Minima,MinIdx] = findpeaks(DataInv);
The true minima will then be:
Minima = Data(MinIdx);
The index values also allow you to determine the times the maxima and minima occurred.
댓글 수: 9
Christos-Nikolaos Zacharopoulos
2018년 2월 27일
Hi, I know that this is an old question, but why is the signal inverted using : DataInv = 1.01*max(Data) - Data; Cheers,
Star Strider
2018년 2월 27일
For some reason, it was important that the inverted waveform be greater than zero. (That was 5½ years ago, so I don’t remember the details.)
That’s likely not necessary for every signal. If you want the minima, just negate the original signal and use the indices findpeaks returns in the second output to get the values of the original signal.
I you have R2017b, the islocalmin function is also an option to get the minima without inverting the signal.
추가 답변 (5개)
Steven Lord
2021년 3월 4일
For more recent releases take a look at the islocalmin, islocalmax, and (perhaps) detrend functions.
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Image Analyst
2012년 7월 22일
편집: Image Analyst
2012년 7월 22일
If you have the Image Processing Toolbox, you can use imregionmax() and imregionalmin(). Do you have that toolbox? If you do that would be the simplest because it's just simply one line of code to find either the maxs or the mins.
You can also do it by seeing where the morphological max or min (performed by imdilate() and imerode() respectively) equals the original array. But again, that requires the Image Processing Toolbox.
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Randy82
2014년 8월 13일
I have one question: Why do i have to multiply max(Data) with a factor 1.01?
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Prithisha K
2021년 9월 8일
Set the prominence window value to 25. Then increase the min.prominence value untill there are exactly 9 minima found.
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