clear; clc;

[~, ~, raw] = xlsread("C:\Users\user\Documents\Matlab335\y9999.xlsx");
raw(1 : 3, :) = [];

prices = [raw{:, 2}];         % cell2mat(raw(:, 2))
dates = datetime(raw(:, 1));
plot(dates, prices);

daily_return_rates = diff(log(prices));
figure;
plot(dates(2 : end), daily_return_rates);
mask = daily_return_rates < -0.05;
dates([false, mask])
daily_return_rates(mask)