Find the formula and sketch the graph of sleepiness over the course of a day due to the ultradian rhythm.
Sleepiness has two cycles, a circadian rhythm with a period of approximately 24 hours and an ultradian rhythm with a period of approximately 4 hours. Both have phase 0 (starting at midnight) and average 0, but the amplitude of the circadian rhythm is 1.0 sleepiness unit and the ultradian is 0.4 sleepiness unit.