$title Calendar Function Examples (CALENDAR,SEQ=183)

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Calendar Function Examples

GAMS Development Corporation, Formulation and Language Example.

The Date and Time Functions are:

      Serial = Jstart     (start of Gams Job)
      Serial = JNow       (current date/time stamp)

      Year   = GYear  (serial)
      Month  = GMonth (serial)
      Day    = GDay   (serial)
      Hours  = GHour  (serial)
      Minute = GMinute(serial)
      Second = GSecond(serial)
      DoW    = GDoW   (serial)   (1=Monday,2=Tuesday,..)
      Leap   = GLeap  (serial)   (0=no leap year, 1=leap year)

      DSerial = JDate(Year,Month,Day)         (full days)
      TSerial = JTime(Hour,Minute,Second);    (fraction of day)

      Inputs to the J(ulian) Functions are Gregorian dates and the
      G(regorian) Functions are days since January 1, 1900.

   The Jstart/Jnow return a serial number that measures the time
   elapsed since January 1, 1900, at 00:00:00 in days.

   Note the relationship below:

   jstart == jdate(gyear(jstart),gmonth (jstart),gday   (jstart))
           + Jtime(ghour(jstart),gminute(jstart),gsecond(jstart))

Keywords: GAMS language features, calendar functions
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Scalar
   start 'date + time at start of GAMS job'
   now   'current date + time';

Scalar
   year, month, day,  hour, minute, second, dow,
   leap, date,  time, diff, sdate,  stime,  diff;

start = jstart;
now   = jnow;

year = gyear(start); month  = gmonth (start); day    = gday   (start);
hour = ghour(start); minute = gminute(start); second = gsecond(start);
dow  = gdow (start);
leap = gleap(start);
display start, now, year, month, day, hour, minute, second, dow, leap;

date  = jdate(year,month,day);
time  = jtime(hour,minute,second);
diff  = start - (date + time);
sdate = floor(start);
stime = mod(start,1);
display date, time, diff, sdate, stime;

* get resolution of jnow by looking at the first 5 changes
Scalar test, i, old, new, sec;
new = jnow;

for(i = 1 to 5,
   old = new;
   while(old = new, new = jnow;);   // burn time until Jnow changes
   test = new - old;
   display test;
   sec  = gsecond(new) - gsecond(old);
   display sec;
);

* now we want to know when to celebrate the year 2000
Scalar s2000, days2000, hours2000, min2000, sec2000;

s2000     = jdate(2000,1,1) - jnow;
days2000  = floor(s2000);
hours2000 = floor(mod(s2000,1)*24);
min2000   = floor(mod(s2000*24,1)*60);
sec2000   = mod(s2000*24*60,1)*60;
display 'all truncated numbers', days2000, hours2000, min2000, sec2000;

days2000  = s2000;
hours2000 = mod(days2000,1)*24;
min2000   = mod(hours2000,1)*60;
sec2000   = mod(min2000,1)*60;
display 'all fractional numbers', days2000, hours2000, min2000, sec2000;

* print a calendar for a number of years
Set
   w / Mon, Tue, Wed, Thu, Fri, Sat, Sun /
   m / January, February, March, April, May, June, July, August, September, October, November, December /
   y / 1997, 1998, 1999, 2000 /;

Parameter
   dim(y,m) 'days in month'
   ym(y)    'year'
   sm(m)    'next month';

sm(m--1) = ord(m);
ym(y)    = ord(y) + 1996;
dim(y,m) = jdate(ym(y) + (card(m) = ord(m)),sm(m),1) - jdate(ym(y),ord(m),1)
display sm, dim;

File calendar;
put  calendar @12 'C a l e n d a r' /
              @12 '---------------' /;
loop(y,
   put / / @13 'Year = ' y.tl
   loop(m,
      put / / @15 ,m.tl /;
      loop(w, put w.tl:>5;);
      old = 1;
      for(i = 1 to dim(y,m),
         date  = jdate(ym(y),ord(m),i);
         put$old / ;
         put @((gdow(date) - 1)*5 + 1) i:5:0;
         old = calendar.cc >= card(w)*5;
      );
   );
);

* print a calendar from today for 400 days
File calendar;
put / / / / @12 'C a l e n d a r' /
            @12 '---------------' /;
month = 0;
for(i = jstart to jstart + 400,
   if(month <> gmonth(i),
      month = gmonth(i);
      put / / @15 ,month:2:0 '/' gyear(i):4:0 /;
      loop(w, put w.tl:>5;);
      put /;
   );
   put$(calendar.cc >= card(w)*5) /;
   put @((gdow(i) - 1)*5 + 1) gday(i):5:0;
);