Ch3_calendar and clocks

Ch3_calendar and clocks - Chapter 3 Calendars and Clocks...

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Chapter 3 Calendars and Clocks Computations involving time, dates, biorhythms and Easter. Calendars are interesting mathematical objects. The Gregorian calendar was first proposed in 1582. It has been gradually adopted by various countries and churches over the four centuries since then. The British Empire, including the colonies in North America, adopted it in 1752. Turkey did not adopt it until 1923. The Gregorian calendar is now the most widely used calendar in the world, but by no means the only one. In the Gregorian calendar, a year y is a leap year if and only if y is divisible by 4 and not divisible by 100, or is divisible by 400. In Matlab the following expression must be true . For example, 2000 was a leap year, but 2100 will not be a leap year. This rule implies that the Gregorian calendar repeats itself every 400 years. In that 400-year period, there are 97 leap years, 4800 months, 20871 weeks, and 146097 days. The average number of days in a Gregorian calendar year is 365 + 97 400 = 365 . 2425. The Matlab function clock returns a six-element vector c with elements c(1) = year c(2) = month c(3) = day c(4) = hour c(5) = minute c(6) = seconds Copyright c ± 2009 Cleve Moler Matlab R ± is a registered trademark of The MathWorks, Inc. TM August 8, 2009 1
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2 Chapter 3. Calendars and Clocks The first five elements are integers, while the sixth element has a fractional part that is accurate to milliseconds. The best way to print a clock vector is to use fprintf or sprintf with a specified format string that has both integer and floating point fields. f = ’%6d %6d %6d %6d %6d %9.3f\n’ I am writting this on May 22, 2007, at about 7:30pm, so c = clock; fprintf(f,c); produces 2007 5 22 19 31 54.015 In other words, year = 2007 month = 5 day = 22 hour = 19 minute = 31 seconds = 54.015 The Matlab functions datenum , datevec , datestr , and weekday use clock and facts about the Gregorian calendar to facilitate computations involving calendar dates. Dates are represented by their serial date number , which is the number of days since the theoretical time and day over 20 centuries ago when clock would have been six zeroes. We can’t pin that down to an actual date because different calendars would have been in use at that time. The function
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Ch3_calendar and clocks - Chapter 3 Calendars and Clocks...

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