Finding local minimums/maximums for a set of data

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Si14 2012-7-21

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评论： Umesh Gautam 2023-5-11

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.

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Steev Mathew 2021-3-4

Thanks! This helped me a lot. I was looking for a way to filter out noise from my data.

Anupama V 2022-11-6

How to find the valley of a ppg signal?(secondary peak of a signal)

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Star Strider 2012-7-22

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编辑：Star Strider 2012-7-22

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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.

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Christos-Nikolaos Zacharopoulos 2018-2-27

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 2018-2-27

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.

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Steven Lord 2021-3-4

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For more recent releases take a look at the islocalmin, islocalmax, and (perhaps) detrend functions.

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Si14 2012-7-26

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在 MATLAB Online 中打开

Thank you guys for your responses. I am using the following and it works nice:

[Maxima,MaxIdx] = findpeaks(Data);
DataInv = 1.01*max(Data) - Data;
[Minima,MinIdx] = findpeaks(DataInv);
Minima = Data(MinIdx);

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Star Strider 2012-7-26

Thank you for accepting my answer!

Umesh Gautam 2023-5-11

It is working great.

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Image Analyst 2012-7-22

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编辑：Image Analyst 2012-7-22

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.