Evolve
Running a ANUGA model involves five basic steps:
Here we describe the last step, how to run (evolve) the model for a specified amount of time.
Evolving the Model
In addition to evolving the model, it would good to be able to interact with the evolving model. This
is all provided by the evolve
method
of the Domain object.
Suppose we have created and set up a Domain by completing the first 4 basic steps. For example here is such a setup for a domain object called domain:
>>> domain = anuga.rectangular_cross_domain(10,5)
>>> domain.set_quantity('elevation', function = lambda x,y : x/10)
>>> domain.set_quantity('stage', expression = "elevation + 0.2" )
>>> Br = anuga.Reflective_boundary(domain)
>>> domain.set_boundary({'left' : Br, 'right' : Br, 'top' : Br, 'bottom' : Br})
To evolve the model we would use the domain’s evolve method, using the following code:
>>> for t in domain.evolve(yieldstep=1.0, finaltime=10.0):
>>> pass
This will run the model from time=0 to the finaltime = 10.0. The method will yield to the for loop every yieldstep = 1. By default the state of the simulation will be saved to a file (by default named domain.sww) every yieldstep, in this case every 1 second of simulation time.
As the evolve construct provides a for loop (via the python yield construct) it is possible
to include extra code within the loop. A typical evolve loop can provide some printed feedback
using the print_timestepping_statistics
method, i.e.,
>>> for t in domain.evolve(yieldstep=1.0, finaltime=10.0):
>>> domain.print_timestepping_statistics()
Time = 0.0000 (sec), steps=0 (33s)
Time = 1.0000 (sec), delta t in [0.00858871, 0.01071429] (s), steps=111 (0s)
Time = 2.0000 (sec), delta t in [0.00832529, 0.00994060] (s), steps=110 (0s)
Time = 3.0000 (sec), delta t in [0.00901413, 0.00993095] (s), steps=106 (0s)
Time = 4.0000 (sec), delta t in [0.00863985, 0.00963487] (s), steps=109 (0s)
Time = 5.0000 (sec), delta t in [0.00887345, 0.00990731] (s), steps=106 (0s)
Time = 6.0000 (sec), delta t in [0.00934142, 0.00988233] (s), steps=104 (0s)
Time = 7.0000 (sec), delta t in [0.00904828, 0.00970252] (s), steps=107 (0s)
Time = 8.0000 (sec), delta t in [0.00917360, 0.00985509] (s), steps=106 (0s)
Time = 9.0000 (sec), delta t in [0.00925747, 0.00984041] (s), steps=104 (0s)
Time = 10.0000 (sec), delta t in [0.00927581, 0.00973202] (s), steps=106 (0s)
During the evolution the yieldsteps are fixed but to maintain stability of the simulation, the underlying computation uses inner evolve timesteps which are generally much smaller than the yieldstep. The number of these inner evolve timesteps are reported as steps and the range of the sizes of these evolve timesteps are reported as the delta t.
Duration instead of finaltime
It can also be convenient to evolve for a specific duration. In this case we replace the finaltime argument with duration. I.e. let us continue the evolution for 7 seconds with yieldstep now set to 2 seconds.
>>> for t in domain.evolve(yieldstep=2.0, duration=7.0):
>>> domain.print_timestepping_statistics()
Time = 12.0000 (sec), delta t in [0.00932516, 0.00982159] (s), steps=209 (63s)
Time = 14.0000 (sec), delta t in [0.00941363, 0.00981322] (s), steps=210 (0s)
Time = 16.0000 (sec), delta t in [0.00944121, 0.00979934] (s), steps=208 (0s)
Time = 17.0000 (sec), delta t in [0.00945517, 0.00978655] (s), steps=105 (0s)
Outputstep
Sometimes it is necessary to interact with the evolution using a small yieldstep (such as controlling a hydraulic structure). In this case the sww file stored at each yieldstep can become prohibitively large.
Instead you can save the state every outputstep time interval, while still interacting every yieldstep interval.
For instance. let us continue the evolution, but now with a smaller yieldstep of 0.5 seconds, but with output to domain.sww every 2 seconds.
>>> for t in domain.evolve(yieldstep=0.5, outputstep=2.0, duration=4.0):
>>> domain.print_timestepping_statistics()
Time = 17.5000 (sec), delta t in [0.00964414, 0.00977317] (s), steps=52 (650s)
Time = 18.0000 (sec), delta t in [0.00946685, 0.00972477] (s), steps=53 (0s)
Time = 18.5000 (sec), delta t in [0.00953534, 0.00965620] (s), steps=53 (0s)
Time = 19.0000 (sec), delta t in [0.00955560, 0.00976215] (s), steps=52 (0s)
Time = 19.5000 (sec), delta t in [0.00947717, 0.00955428] (s), steps=53 (0s)
Time = 20.0000 (sec), delta t in [0.00955552, 0.00966630] (s), steps=53 (0s)
Time = 20.5000 (sec), delta t in [0.00951811, 0.00975266] (s), steps=52 (0s)
Time = 21.0000 (sec), delta t in [0.00948645, 0.00957223] (s), steps=53 (0s)
Typical situations could be yieldstep = 1.0 and outputstep=300. In this case the sww file will be 300 times smaller than just using yieldstep for output.
Start Time
By default the evolution starts at time 0.0. To set another start time, simply use
set_starttime
before the evolve loop, i.e.
>>> domain.set_starttime(3600*24)
to set the start time one day in the past (from ANUGA’s zero time). This can be used to allow the model to “burn in” before starting the evolution proper.
Start times with DateTime and Timezones
To work with dates, times and timezones we can use the python module datetime. to setup a date and time (and timezone) associated with ANUGA’s starttime time.
Once again let’s suppose we have setup a domain via:
>>> import anuga
>>> from datetime import datetime
>>> domain = anuga.rectangular_cross_domain(10,5)
>>> domain.set_quantity('elevation', function = lambda x,y : x/10)
>>> domain.set_quantity('stage', expression = "elevation + 0.2" )
>>> Br = anuga.Reflective_boundary(domain)
>>> domain.set_boundary({'left' : Br, 'right' : Br, 'top' : Br, 'bottom' : Br})
By default ANUGA uses a UTC as the default timezone for the domain.
We can change it via set_timezone
>>> domain.set_timezone('Australia/Sydney')
A list of timezones names can be found on Wikipedia.
Suppose we want to start the model at 18:45 on the 21st July 2021. Use the datetime module to setup this date, and the set the start time, as follows:
>>> from datetime import datetime
>>> starttime = datetime(2021, 7, 21, 18, 45)
>>> domain.set_starttime(starttime)
Suppose we want to evolve until 19:00 on the 21st July 2021. Use datetime to setup this finaltime:
>>> finaltime = datetime(2021, 7, 21, 19, 0)
And now evolve the model. Note the use of the datetime = True argument for the
print_timestepping_statisitics
procedure.
>>> for t in domain.evolve(yieldstep=300, finaltime=finaltime):
>>> domain.print_timestepping_statistics(datetime=True)
DateTime: 20210721 18:45:00+1000, steps=0 (0s)
DateTime: 20210721 18:50:00+1000, delta t in [0.00832571, 0.01071429] (s), steps=31233 (10s)
DateTime: 20210721 18:55:00+1000, delta t in [0.00959070, 0.00964172] (s), steps=31205 (10s)
DateTime: 20210721 19:00:00+1000, delta t in [0.00959070, 0.00964172] (s), steps=31205 (10s)
Default zero time
We use unix timestamp as our underlying absolute time. So time = 0 actually corresponds to Jan 1st 1970 UTC.
For instance going back to an earlier example which uses the default timezone (UTC) and 0 start time.
(Compare the output with datetime = True and datetime = False in the
print_timestepping_statistics
procedure.)
>>> import anuga
>>> domain = anuga.rectangular_cross_domain(10,5)
>>> domain.set_quantity('elevation', function = lambda x,y : x/10)
>>> domain.set_quantity('stage', expression = "elevation + 0.2" )
>>> Br = anuga.Reflective_boundary(domain)
>>> domain.set_boundary({'left' : Br, 'right' : Br, 'top' : Br, 'bottom' : Br})
>>>
>>> for t in domain.evolve(yieldstep=1, finaltime=5):
>>> domain.print_timestepping_statistics(datetime=True)
DateTime: 19700101 00:00:00+0000, steps=0 (10s)
DateTime: 19700101 00:00:01+0000, delta t in [0.00858871, 0.01071429] (s), steps=111 (0s)
DateTime: 19700101 00:00:02+0000, delta t in [0.00832529, 0.00994060] (s), steps=110 (0s)
DateTime: 19700101 00:00:03+0000, delta t in [0.00901413, 0.00993095] (s), steps=106 (0s)
DateTime: 19700101 00:00:04+0000, delta t in [0.00863985, 0.00963487] (s), steps=109 (0s)
DateTime: 19700101 00:00:05+0000, delta t in [0.00887345, 0.00990731] (s), steps=106 (0s)
Note that the date is 1st Jan 1970, starting at time 0:00, incrementing by 1 sec and the UTC offset is +0000 (ie the timezone is UTC).
Useful Domain methods

Evolve method from Domain class. 
Print time stepping statistics 


Set the starttime for the evolution 
Set timezone for domain 