Find Middle of square wave

Question

Russell Senior 2020-4-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/514873-find-middle-of-square-wave

评论： Star Strider 2020-4-2

I can find the rising edge and falling edge of a square wave, any thoughts on how to find the middle of an arbitrary square wave? I created a simple code using a logical array that finds the rising edges and falling edges, but I can't think of a good way to find the middle of the square. Ideas?

Edit: I'd like to avoid using a for loop. Speed is important since this will be used to process a few GB of data.

clear all
close all
t = 0:100;
x = false(size(t));
x(2:10) = true;
x(25:30) = true;
x(50:75) = true;
x(90:end) = true;
rising = x > [x(1) x(1:end-1)];
falling = x < [x(1) x(1:end-1)];
subplot(3,1,1)
plot(t,x)
subplot(3,1,2)
plot(t,rising,'r')
subplot(3,1,3)
plot(t,falling,'k')

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Answer 1

Star Strider 2020-4-2

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https://ww2.mathworks.cn/matlabcentral/answers/514873-find-middle-of-square-wave#answer_423601

Use the islocalmax function (R2017b and later):

This code plots green upward-pointing triangles at the centre of each pulse:

t = 0:100;
x = false(size(t));
x(2:10) = true;
x(25:30) = true;
x(50:75) = true;
x(90:end) = true;
rising = x > [x(1) x(1:end-1)];
falling = x < [x(1) x(1:end-1)];
ctr = islocalmax(x, 'FlatSelection','center');          % Added
subplot(3,1,1)
plot(t,x)
hold on
plot(t(ctr), x(ctr), 'g^')                              % Added
hold off
subplot(3,1,2)
plot(t,rising,'r')
subplot(3,1,3)
plot(t,falling,'k')