DOOMSDAY
Day of Week for Given Date

DOOMSDAY is a FORTRAN90 library which is given the year, month and day of a date, and uses John Conway's doomsday algorithm to determine the corresponding day of the week.

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Languages:

DOOMSDAY is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version and a Python version.

Related Data and Programs:

ANALEMMA, a FORTRAN90 program which evaluates the equation of time, a formula for the difference between the uniform 24 hour day and the actual position of the sun, based on a program by Brian Tung.

CALENDAR_NYT, a FORTRAN90 library which shows the correspondence between dates and the New York Times volume and issue number;

CALENDAR_RD, a C++ program which computes the representation of a given date in a number of calendrical systems, by Edward Reingold and Nachum Dershowitz

CALPAK, a FORTRAN90 library which makes various calendar calculations;

DATES, a dataset directory which contains lists of dates in various calendar systems.

WEEKDAY, a FORTRAN90 library which determines the day of the week for a given day.

Reference:

1. Lewis Carroll (Charles Dodgson),
   To Find the Day of the Week for Any Given Date,
   Nature, 31 March 1887.
2. John Conway,
   Tomorrow is the Day After Doomsday,
   Eureka,
   Volume 36, October 1973, pages 28-31.
3. Gary Meisters,
   Lewis Carroll's Day-of-the-Week Algorithm,
   Math Horizons,
   November 2002, pages 24-25.

Source Code:

• doomsday.f90, the source code.

Examples and Tests:

• doomsday_test.f90, a sample calling program.
• doomsday_test.txt, the output file.

List of Routines:

• DOOMSDAY_GREGORIAN: weekday given any date in Gregorian calendar.
• I4_MODP returns the nonnegative remainder of I4 division.
• I4_WRAP forces an I4 to lie between given limits by wrapping.
• TIMESTAMP prints the current YMDHMS date as a time stamp.
• WEEKDAY_TO_NAME_COMMON returns the name of a Common weekday.
• WEEKDAY_VALUES returns the day of the week for various dates.
• YEAR_IS_LEAP_GREGORIAN returns TRUE if the Gregorian year was a leap year.

You can go up one level to the FORTRAN90 source codes.