WEEKDAY
Determine the Day of the Week

WEEKDAY is a FORTRAN77 library which can determine the day of the week corresponding to a given date; for instance, the battle of Hastings, on 14 October 1066 (Julian Calendar!), was a Saturday.

Licensing:

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

Languages:

WEEKDAY is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version.

Related Data and Programs:

ANALEMMA, a FORTRAN77 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, creating data that can be plotted by gnuplot, based on a C 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, Nachum Dershowitz

CALPAK, a FORTRAN90 library which makes various calendar calculations;

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

DOOMSDAY, a FORTRAN77 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.

TEST_VALUES, a FORTRAN77 library which supplies test values of various mathematical functions.

Reference:

1. Lewis Carroll (Charles Dodgson),
   To Find the Day of the Week for Any Given Date,
   Nature, 31 March 1887.
2. Gary Meisters,
   Lewis Carroll's Day-of-the-Week Algorithm,
   Math Horizons,
   November 2002, pages 24-25.
3. Edward Reingold, Nachum Dershowitz,
   Calendrical Calculations: The Millennium Edition,
   Cambridge University Press, 2001,
   ISBN: 0-521-77752-6,
   LC: CE12.R45.
4. Edward Richards,
   Mapping Time, The Calendar and Its History,
   Oxford, 1999,
   ISBN: 0-19-850413-6,
   LC: CE11.R5.

Source Code:

• weekday.f, the source code.
• weekday.sh, commands to compile the source code.

Examples and Tests:

• weekday_prb.f, a sample calling program.
• weekday_prb.sh, commands to compile and run the sample program.
• weekday_prb_output.txt, the output file.

List of Routines:

• DIGIT_TO_CH returns the character representation of a decimal digit.
• I4_MODP returns the positive remainder when I is divided by J.
• I4_TO_S_LEFT converts an integer to a left-justified string.
• I4_TO_S_ZERO converts an integer to a string, with zero padding.
• I4_WRAP forces an integer to lie between given limits by wrapping.
• JED_TO_WEEKDAY computes the day of the week from a JED.
• S_CAT concatenates two strings to make a third string.
• 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.
• Y_COMMON_TO_ASTRONOMICAL converts a Common year to an Astronomical year.
• YMD_TO_S_COMMON writes a Common YMD date into a string.
• YMD_TO_WEEKDAY_COMMON returns the weekday of a Common YMD date.
• YMDF_COMPARE compares two YMDF dates.
• YMDF_TO_JED_COMMON converts a Common YMDF date to a JED.
• YMDF_TO_JED_GREGORIAN converts a Gregorian YMDF date to a JED.
• YMDF_TO_JED_JULIAN converts a Julian YMDF date to a JED.

You can go up one level to the FORTRAN77 source codes.