How to find the average of y over a range of x?

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Marcella Roth 2022-4-25

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评论： Voss 2022-4-26

Hi Everyone,

I have a dataset containing two variables, x (time) and y (amplitude). I want to find the average amplitude over a given time range. I'm very much a beginner with MatLab and any help would be appreciated!

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Answer 1

Voss 2022-4-25

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1705080-how-to-find-the-average-of-y-over-a-range-of-x#answer_950810

在 MATLAB Online 中打开

% some times, x:

x = 0:0.01:9

x = 1×901

0 0.0100 0.0200 0.0300 0.0400 0.0500 0.0600 0.0700 0.0800 0.0900 0.1000 0.1100 0.1200 0.1300 0.1400 0.1500 0.1600 0.1700 0.1800 0.1900 0.2000 0.2100 0.2200 0.2300 0.2400 0.2500 0.2600 0.2700 0.2800 0.2900

% some amplitudes, y:

y = sin(x)

y = 1×901

0 0.0100 0.0200 0.0300 0.0400 0.0500 0.0600 0.0699 0.0799 0.0899 0.0998 0.1098 0.1197 0.1296 0.1395 0.1494 0.1593 0.1692 0.1790 0.1889 0.1987 0.2085 0.2182 0.2280 0.2377 0.2474 0.2571 0.2667 0.2764 0.2860

% plot y vs x to visualize (see plot below):

plot(x,y)

% a time range, x_min and x_max:

x_min = 2.2;

x_max = 2.9;

% find the average value of y, where x is within the interval [x_min,x_max]:

y_avg = mean(y(x >= x_min & x <= x_max))

y_avg = 0.5460

% plot that too:

hold on

plot([x_min x_max],[y_avg y_avg])

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Marcella Roth 2022-4-26

Thank you so much! Is there a way to only include positive numbers in the average?

Voss 2022-4-26

在 MATLAB Online 中打开

You're welcome!

Yes, this will average just the positive numbers within the given range:

% some times, x:
x = 0:0.01:9;
% some amplitudes, y:
y = sin(x);
% a time range, x_min and x_max:
% (pick a range that includes some non-positive y values)
x_min = 2;
x_max = 6;
% find the average value of y, where x is within the interval [x_min,x_max]
% and y is positive:
y_avg = mean(y(x >= x_min & x <= x_max & y > 0))
y_avg = 0.5117