Easter date gauss algorithm (#2010)

* Added gauss easter algorithm * Fixes in easter algorithm * Commit suggestions
TheAlgorithms · May 19, 2020 · 243100165800d5f4be46b6234c4888e34eb63e60 · 2431001
1 parent c906ba8
commit 243100165800d5f4be46b6234c4888e34eb63e60
Unified Split

Showing with 59 additions and 0 deletions.

+59 −0 other/gauss_easter.py
diff --git a/other/gauss_easter.py b/other/gauss_easter.py
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+"""
+https://en.wikipedia.org/wiki/Computus#Gauss'_Easter_algorithm
+"""
+import math
+from datetime import datetime, timedelta
+
+
+def gauss_easter(year: int) -> datetime:
+    """
+    Calculation Gregorian easter date for given year
+
+    >>> gauss_easter(2007)
+    datetime.datetime(2007, 4, 8, 0, 0)
+
+    >>> gauss_easter(2008)
+    datetime.datetime(2008, 3, 23, 0, 0)
+
+    >>> gauss_easter(2020)
+    datetime.datetime(2020, 4, 12, 0, 0)
+
+    >>> gauss_easter(2021)
+    datetime.datetime(2021, 4, 4, 0, 0)
+    """
+    metonic_cycle = year % 19
+    julian_leap_year = year % 4
+    non_leap_year = year % 7
+    leap_day_inhibits = math.floor(year / 100)
+    lunar_orbit_correction = math.floor((13 + 8 * leap_day_inhibits) / 25)
+    leap_day_reinstall_number = leap_day_inhibits / 4
+    secular_moon_shift = (
+        15 - lunar_orbit_correction + leap_day_inhibits - leap_day_reinstall_number
+    ) % 30
+    century_starting_point = (4 + leap_day_inhibits - leap_day_reinstall_number) % 7
+
+    # days to be added to March 21
+    days_to_add = (19 * metonic_cycle + secular_moon_shift) % 30
+
+    # PHM -> Paschal Full Moon
+    days_from_phm_to_sunday = (
+        2 * julian_leap_year
+        + 4 * non_leap_year
+        + 6 * days_to_add
+        + century_starting_point
+    ) % 7
+
+    if days_to_add == 29 and days_from_phm_to_sunday == 6:
+        return datetime(year, 4, 19)
+    elif days_to_add == 28 and days_from_phm_to_sunday == 6:
+        return datetime(year, 4, 18)
+    else:
+        return datetime(year, 3, 22) + timedelta(
+            days=int(days_to_add + days_from_phm_to_sunday)
+        )
+
+
+if __name__ == "__main__":
+    for year in (1994, 2000, 2010, 2021, 2023):
+        tense = "will be" if year > datetime.now().year else "was"
+        print(f"Easter in {year} {tense} {gauss_easter(year)}")