# Time vector representation
# Time has a periodic nature due to the rotation of the earth and the position of the sun.
# This affects human behavior in various ways.
#
# Seasonality ... periodicity in a year (seasonal distinction)
# Daily periodicity ... periodicity in a day (distinction between day and night)
# Day of the week ... periodicity in a week (distinction between weekdays and holidays)
#
# When dealing with these, it is desirable to vectorize with periodicity in mind.
# That is, at 23:59 on a given day, it is desirable that the value is close to 00:00 on the next day.
# To achieve this, the time is represented as a combination of cos and sin.
