easter←{ ⍝ Easter Sunday in year ⍵. G←1+19|⍵ ⍝ year "golden number" in 19-year Metonic cycle. C←1+⌊⍵÷100 ⍝ Century: for example 1984 → 20th century. X←¯12+⌊C×3÷4 ⍝ number of years in which leap year omitted. Z←¯5+⌊(5+8×C)÷25 ⍝ synchronises Easter with moon's orbit. S←(⌊(5×⍵)÷4)-X+10 ⍝ find Sunday. E←30|(11×G)+20+Z-X ⍝ Epact. F←E+(E=24)∨(E=25)∧G>11 ⍝ (when full moon occurs). N←(30×F>23)+44-F ⍝ find full moon. N←N+7-7|S+N ⍝ advance to Sunday. M←3+N>31 ⍝ month: March or April. D←N-31×N>31 ⍝ day within month. ↑10000 100 1+.×⍵ M D ⍝ yyyymmdd. } code_colours test script Back to: notes Back to: Workspaces