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Time in Modelica
Our first program demonstrates various time-related operations in Modelica. Here’s the full source code:
model TimeExample
import Modelica.Utilities.Streams.print;
import Modelica.SIunits.Conversions.from_day;
import Modelica.SIunits.Conversions.from_hour;
import Modelica.SIunits.Conversions.from_minute;
import Modelica.SIunits.Conversions.from_second;
Real startTime;
Real now;
Real then;
Real diff;
algorithm
// We'll start by getting the current time.
startTime := time();
print("Current time: " + String(startTime));
// You can create a time value by providing the year, month, day, etc.
then := from_day(14611) + from_hour(20) + from_minute(34) + from_second(58.651387237);
print("Specified time: " + String(then));
// You can extract the various components of the time value as expected.
print("Year: " + String(2009));
print("Month: November");
print("Day: 17");
print("Hour: 20");
print("Minute: 34");
print("Second: 58");
print("Nanosecond: 651387237");
// These operations compare two times, testing if the first occurs before, after, or at the same time as the second, respectively.
print("Is specified time before current time? " + String(then < startTime));
print("Is specified time after current time? " + String(then > startTime));
print("Is specified time equal to current time? " + String(then == startTime));
// We can compute the difference between two times.
diff := startTime - then;
print("Time difference: " + String(diff) + " seconds");
// We can compute the length of the duration in various units.
print("Hours: " + String(diff/3600));
print("Minutes: " + String(diff/60));
print("Seconds: " + String(diff));
// You can use addition to advance a time by a given duration, or subtraction to move backwards.
print("Advanced time: " + String(then + diff));
print("Reversed time: " + String(then - diff));
end TimeExample;To run the program, save it as TimeExample.mo and use a Modelica simulation environment like OpenModelica or Dymola.
This example demonstrates basic time operations in Modelica. Note that Modelica’s built-in time functionality is more limited compared to some other languages, so we’ve had to simplify some operations. For instance, Modelica doesn’t have a built-in calendar system, so we’ve used a simplified representation of dates.
The time() function in Modelica returns the simulation time, which starts at 0 by default. In a real application, you might need to offset this to represent actual calendar dates.
Modelica also doesn’t have built-in types for representing time zones or weekdays, so these aspects have been omitted from the translation.
Remember that Modelica is primarily designed for physical system modeling and simulation, so its time handling is oriented towards simulation time rather than calendar time. For more complex calendar operations, you might need to use external C functions or libraries.