Partitioning a regional model

This example shows how a model can be partitioned into submodels. This will allow parallelization when solving the model. The example used is the Hondsrug model. It is partitioned into 3 rectangular parts. In the example we first run the original, unpartitioned model. Then we partition the model and run the resulting simulation. Finally we merge the head output of the submodels into a head array for the whole grid. we print both the heads obtained without partitioning, and the merged heads of the partitioned simulation, ‘ for comparison.

import matplotlib.pyplot as plt

import imod
from imod.mf6.multimodel.partition_generator import get_label_array

Obtain the simulation, write it, run it, and plot some heads. There is a separate example contained in hondsrug that you should look at if you are interested in the model building

tmpdir = imod.util.temporary_directory()

gwf_simulation = imod.data.hondsrug_simulation(tmpdir / "hondsrug_saved")

Write the model and run it (before partitioning, so we can compare if the results are similar).

original_modeldir = tmpdir / "original"

gwf_simulation.write(original_modeldir)
gwf_simulation.run()

Plot the simulation results of the unpartitioned model.

hds_original = gwf_simulation.open_head()

fig, ax = plt.subplots()

hds_original.sel(layer=3).isel(time=6).plot(ax=ax)
ax.set_title("hondsrug original ")

Text(0.5, 1.0, 'hondsrug original ')

Now we partition the Hondsrug model

idomain = gwf_simulation["GWF"].domain
number_partitions = 16
submodel_labels = get_label_array(gwf_simulation, number_partitions)

plot the partitioning array. It shows how the model will be partitioned.

fig, ax = plt.subplots()
submodel_labels.plot(ax=ax)
ax.set_title("hondsrug partitioning geometry")

split_simulation = gwf_simulation.split(submodel_labels)

Now we write and run the partitioned model

split_modeldir = tmpdir / "split"

split_simulation.write(split_modeldir)
split_simulation.run()

Load and plot the simulation results. Also plot the differences with the original model

hds_split = split_simulation.open_head()["head"]
fig, ax = plt.subplots()
hds_split.sel(layer=3).isel(time=6).plot(ax=ax)
ax.set_title("hondsrug partitioned ")

diff = hds_split - hds_original
diff_for_plot = diff.max(dim=["time", "layer"])
fig, ax = plt.subplots()
diff_for_plot.plot(ax=ax)
ax.set_title("hondsrug diff ")

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Text(0.5, 1.0, 'hondsrug diff ')