find max & min

If I want to choose one cycle. The cycle must have criteria : largest distance maximum & minimum, 3 point cross X axis. Thank you very much in advanced.

[Turlough Hughes]

What do you mean by one cycle? Are you looking for the maximum change in y given a change in x of 3?

Answer 1

[Image Analyst]

This will do it:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;

s = load('data.mat')
data = s.data;
hFig = figure;
plot(data, 'b-', 'LineWidth', 2)
grid on;
xlabel('Index', 'FontSize', fontSize);
ylabel('Signal', 'FontSize', fontSize);
% Maximizxe the window.
hFig.WindowState = 'maximized';

% Find the max
[maxValue, indexOfMax] = max(data)
% Find the min
[minValue, indexOfMin] = min(data)

% Find out where the signal last crosses 0 before the peak
% First set after the peak to infinity so we do not find that.
tempSignal = data;
tempSignal(indexOfMax:end) = inf;
indexLeft = find(tempSignal < 0, 1, 'last')
% Plot a red spot there.
hold on;
plot(indexLeft, data(indexLeft), 'r.', 'MarkerSize', 40);

% Find out where the signal first crosses 0 after the max peak on the right side.
% First set before the valley to infinity so we do not find the peak.
tempSignal = data;
tempSignal(1 : indexOfMax) = inf;
indexMiddle = find(tempSignal < 0, 1, 'first')
% Plot a red spot there.
hold on;
plot(indexMiddle, data(indexMiddle), 'r.', 'MarkerSize', 40);

% Find out where the signal first crosses 0 after the min peak (the biggest valley).
% First set before the valley to -infinity so we do not find the peak.
tempSignal = data;
tempSignal(1 : indexOfMin) = -inf;
indexRight = find(tempSignal > 0, 1, 'first')
% Plot a red spot there.
hold on;
plot(indexRight, data(indexRight), 'r.', 'MarkerSize', 40);

[Arief Kus]

Thank you very much for your help.

[Image Analyst]

You're welcome. Can you "Accept this answer" now by clicking the link?

[Arief Kus]

Done. I am really sorry for late in clicking "Accept this answer".

[Arief Kus]

If I have X and Y data. I want to choose one cycle. The cycle must have criteria : largest distance maximum & minimum, 3 point cross X axis.Thank you very much in advance.