Adv_RK4_2D fails with NotImplementedError from get_horizontal_velocity()

[PandanC]

When setting either of the following in the configuration:
iterative_method = Adv_RK4_2D or adv_iterative_method = Adv_RK4_2D
the program raises a NotImplementedError at runtime:
File "pylag/numerics.pyx", line 1031, in pylag.numerics.AdvRK42DItMethod.step
File "pylag/data_reader.pyx", line 423, in pylag.data_reader.DataReader.get_horizontal_velocity
NotImplementedError
when using the 3D method:
adv_iterative_method = Adv_RK4_3D

[PandanC]

but when using the 3D method:
adv_iterative_method = Adv_RK4_3D, it works

[jimc101]

In what context were you using PyLag? I.e., were you running one of the tutorials? Something else?

[PandanC]

Thank you for your reply. I am running PyLag in parallel with FVCOM's flow field. Previously, I set num_method = operator_split_0, adv_iterative_method = Adv_RK4_3D, and diff_iterative_method = Diff_Visser_1D in the pylag.cfg file, and PyLag worked correctly, providing results for 3D particle motion simulation.

However, now I want to test the 2D advection in PyLag while ignoring diffusion. Initially, I tried setting num_method = standard, iterative_method = Adv_RK4_2D in the configuration file, but the program crashed with the following error:
Traceback (most recent call last):
File "~/anaconda3/envs/build/lib/python3.11/site-packages/pylag/parallel/simulator.py", line 237, in run
self.model.update(self.time_manager.time)
File "pylag/model.pyx", line 537, in pylag.model.OPTModel.update
File "pylag/model.pyx", line 570, in pylag.model.OPTModel.update
File "pylag/numerics.pyx", line 211, in pylag.numerics.StdNumMethod.step
File "pylag/numerics.pyx", line 1031, in pylag.numerics.AdvRK42DItMethod.step
File "pylag/data_reader.pyx", line 423, in pylag.data_reader.DataReader.get_horizontal_velocity
NotImplementedError

Next, I tried setting num_method = operator_split_0, adv_iterative_method = Adv_RK4_2D, and diff_iterative_method = Diff_Const_2D (with horizontal_eddy_diffusivity_constant = 0.0), thinking that this would ignore the diffusion process, but the program still crashed with the same error:
Traceback (most recent call last):
File "~/anaconda3/envs/build/lib/python3.11/site-packages/pylag/parallel/simulator.py", line 237, in run
self.model.update(self.time_manager.time)
File "pylag/model.pyx", line 537, in pylag.model.OPTModel.update
File "pylag/model.pyx", line 570, in pylag.model.OPTModel.update
File "pylag/numerics.pyx", line 211, in pylag.numerics.StdNumMethod.step
File "pylag/numerics.pyx", line 1031, in pylag.numerics.AdvRK42DItMethod.step
File "pylag/data_reader.pyx", line 423, in pylag.data_reader.DataReader.get_horizontal_velocity
NotImplementedError

I would appreciate your help in understanding how to resolve this issue or if I should make any adjustments to my configuration to successfully run the 2D advection simulation.

[jimc101]

You want to do 2D advection but you have a 3D (spatial) input field? In those cases, I do advection in 3D then use depth or height restoring to fix the particle's depth below the free surface or its height above the sea floor respectively. The options are set in the section SIMULATION of the run config. The options are:

[SIMULATION]
depth_restoring = True        # Restores particles to a fixed depth below the free surface
fixed depth = X.X        # The depth below the surface that particles are restored to
height_restoring = False        # Restore particles to a fixed height above the sea bed
fixed_height = X.X        # The fixed height above the bed that particles are restored to

Note that depth_restoring and height_restoring are mutually exclusive. I have just noticed the description of this in the online docs and the example configs contains errors. I will fix these.