How to identify both sides of a flat peak (flat part of a signal)?

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Tomaszzz 2022-7-13

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https://ww2.mathworks.cn/matlabcentral/answers/1758995-how-to-identify-both-sides-of-a-flat-peak-flat-part-of-a-signal

评论： Star Strider 2022-7-15

采纳的回答： Star Strider

signal.mat

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Hi all,

I have the following signal (also attached).

I am trying to find the peaks circles red. The below code does identify all the peaks circled black but i do not understand why it ommits the other side of a flat signal? Can you help please?

load 'signal'
[peak_value,peak_location]= findpeaks(-force_y_r, 'MinPeakProminence',10, 'MinPeakDistance',100);
    peak_value = -peak_value;
 plot(force_y_r, 'LineWidth',1.5); hold on
    plot(peak_location,peak_value,'ko')   

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采纳的回答

Star Strider 2022-7-13

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1758995-how-to-identify-both-sides-of-a-flat-peak-flat-part-of-a-signal#answer_1006370

Use the islocalmin (introduced in R2017b) function instead of findpeaks —

LD = load('signal.mat');

force_y_r = LD.force_y_r;

Lv1 = islocalmin(force_y_r, 'FlatSelection','first', 'MinSeparation',500, 'MinProminence',750);

Lv2 = islocalmin(force_y_r, 'FlatSelection','last', 'MinSeparation',500, 'MinProminence',750);

x = 1:numel(force_y_r);

figure

plot(x, force_y_r)

hold on

plot(x(Lv1), force_y_r(Lv1), '^r')

plot(x(Lv2), force_y_r(Lv2), '^g')

hold off

producing:

It may be necessary to change the name-value pair parameters for other data sets. Use the find function to get numeric indices from the logical vectors.

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Star Strider 2022-7-14

编辑：Star Strider 2022-7-14

As always, my pleasure!

I posted an answer to your follow-up question as well, complete with results, since the indexing turned out to be a bit more complicated that I thought it would be.

EDIT —

The complete revised code is now:

LD = load('signal.mat');

force_y_r = LD.force_y_r;

Lv1 = islocalmin(force_y_r, 'FlatSelection','first', 'MinSeparation',500, 'MinProminence',750);

Lv2 = islocalmin(force_y_r, 'FlatSelection','last', 'MinSeparation',500, 'MinProminence',750);

StartIndices = find(Lv2);

StartIndices = StartIndices(1:end-1);

EndIndices = find(Lv1);

EndIndices = EndIndices(2:end);

for k = 1:numel(StartIndices)

Force{k,:} = force_y_r(StartIndices(k):EndIndices(k));

end

Force

Force1 = Force{1}(1:10) % First 10 Rows

SegmentIndices = table(StartIndices, EndIndices)

x = 1:numel(force_y_r);

figure

plot(x, force_y_r)

hold on

plot(x(EndIndices), force_y_r(EndIndices), '^r')

plot(x(StartIndices), force_y_r(StartIndices), '^g')

hold off

Tomaszzz 2022-7-15

Many thanks @Star Strider , this works perfect!

Star Strider 2022-7-15

As always, my pleasure!

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