#==================================================================
libIGCM_date
This ksh library handles date calculs and convertions in different calendars.
  types of calendars are possible :

  - leap|gregorian|standard (other name leap) :
      The normal calendar. The time origin for the
      julian day in this case is 24 Nov -4713.
  - noleap|365_day :
      A 365 day year without leap years.
  - all_leap|366_day :
      A 366 day year with only leap years.
  - 360d|360_day :
      Year of 360 days with month of equal length.
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function IGCM_date_DaysInYear
* Purpose: Return the number of days in a year
* Usage: IGCM_date_DaysInYear yyyy
         if there is no argument on the command line,
         then assume that a yyyy is being piped in

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function IGCM_date_DaysInMonth
* Purpose: Calculate the number of days in a month
* Usage: IGCM_date_DaysInMonth yyyy mm
         or IGCM_date_DaysInMonth yyyymmdd
         if there are no command line arguments then
         assume that a yyyymmdd is being piped in and read the value.
         if there is only one argument assume it is a yyyymmdd on the command line
         other wise it is a yyyy and mm on the command line
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function IGCM_date_ConvertGregorianDateToJulian
* Purpose: Convert yyyymmdd to yyyyddd
* Usage: IGCM_date_ConvertGregorianDateToJulian 19980429
         if there is no command line argument, then assume that the date
         is coming in on a pipe and use read to collect it

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function IGCM_date_ConvertJulianDateToGregorian()
* Purpose: Convert yyyyddd to yyyymmdd
* Usage: IGCM_date_ConvertJulianDateToGregorian 1998213
         if there is no command line argument, assume one is being
         piped in and read it

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function IGCM_date_AddDaysToJulianDate
* Purpose: Add days to a yyyyddd formatted date
* Usage: IGCM_date_AddDaysToJulianDate 1998312 { ,-}14
         Read the difference from the command lines
         and the date from the command line, or standard input

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function IGCM_date_AddDaysToGregorianDate
* Purpose: Add days to a yyyymmdd formatted date
* Usage: IGCM_date_AddDaysToGregorianDate 19980312 { ,-}14
         Read the difference from the command lines
         and the date from the command line, or standard input

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function IGCM_date_DaysBetweenJulianDate
* Purpose: Calculate the days difference between two dates and reports
           the number days as jul1 - jul2
* Usage: IGCM_date_DaysBetweenJulianDate jul1 jul2
         where julian date is in the form yyyyddd

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function IGCM_date_DaysBetweenGregorianDate ()
* Purpose: Calculate the days difference between two dates and reports
           the number days as grg1 - grg2
* Usage: IGCM_date_DaysBetweenGregorianDate grg1 grg2
         where gregorian date is in the form yyyymmdd

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function IGCM_date_DaysSinceJC ()
* Purpose: Calculate the days difference between a date and 00010101
* Usage: IGCM_date_DaysSinceJC grg1
         where gregorian date is in the form yyyymmdd

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function IGCM_date_DaysInPreviousPeriod ()
* Purpose: Give the numbers of days during the previous prd1 period from grg1 date # OLD create_ts_begin_date
* Usage: IGCM_date_DaysInPreviousPeriod grg1 prd1 [end]
         where grg1 gregorian date is in the form yyyymmdd
         where prd1 period is in the form N[Yy], N[Mm], N[Dd]. N integer
         where [end] is an optionnal keyword to specify grg1 is the end of prd1

#==================================================================
function IGCM_date_DaysInNextPeriod ()
* Purpose: Give the numbers of days during the next prd1 period from grg1 date # OLD create_ts_next_date
* Usage: IGCM_date_DaysInNextPeriod grg1 prd1
         where grg1 gregorian date is in the form yyyymmdd
         where prd1 period is in the form N[Yy], N[Mm], N[Dd]. N integer

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function IGCM_date_DaysInCurrentPeriod ()
* Purpose: Give the numbers of days during the Current prd1 period from grg1 date
* Usage: IGCM_date_DaysInCurrentPeriod grg1 prd1
         where grg1 gregorian date is in the form yyyymmdd
         where prd1 period is in the form N[Yy], N[Mm], N[Dd]. N integer

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function IGCM_date_Check
 * Purpose: Check the present file by comparison with a reference file