.flake8

 [flake8]
 max-line-length=120
-exclude=lbmpy/plot.py
-        lbmpy/session.py
-ignore = W293 W503 W291 E741
+exclude=src/lbmpy/plot.py
+        src/lbmpy/session.py
+ignore = W293 W503 W291 C901 E741

.gitattributes

-lbmpy/_version.py export-subst
+src/lbmpy/_version.py export-subst

.gitignore

 __pycache__
 .ipynb_checkpoints
-.coverage
+.coverage*
 *.pyc
 *.vti
 /build
 /html_doc
 /dist
-/*.egg-info
+*.egg-info
 .cache
 _build
 /.idea
@@ -15,14 +15,15 @@ _local_tmp
 **/pylintrc
 *.bak
 *.tmp
-/lbmpy_tests/db
+/tests/db
 doc/bibtex.json
 /db
-/lbmpy/phasefield/simplex_projection.*.so
-/lbmpy/phasefield/simplex_projection.c
+/src/lbmpy/phasefield/simplex_projection.*.so
+/src/lbmpy/phasefield/simplex_projection.c
 
 # macOS
 **/.DS_Store
+*.uuid
 
 # benchmark database
-/lbmpy_tests/benchmark/db
\ No newline at end of file
+/tests/benchmark/db
\ No newline at end of file

.gitlab-ci.yml

 stages:
   - pretest
   - test
+  - nightly
+  - docs
   - deploy
 
+# --------------------------  Templates ------------------------------------------------------------------------------------
+
+# Base configuration for jobs meant to run at every commit
+.every-commit:
+  rules:
+    - if: $CI_PIPELINE_SOURCE != "schedule"
+
+# Configuration for jobs meant to run on each commit to pycodegen/pystencils/master
+.every-commit-master:
+  rules:
+    - if: '$CI_PIPELINE_SOURCE != "schedule" && $CI_PROJECT_PATH == "pycodegen/lbmpy" && $CI_COMMIT_BRANCH == "master"'
+
+
+# Base configuration for jobs meant to run at a schedule
+.scheduled:
+  rules:
+    - if: $CI_PIPELINE_SOURCE == "schedule"
 
 # --------------------------  Pre Tests --------------------------------------------------------------------------------
 
 # Normal test - runs on every commit all but "long run" tests
 tests-and-coverage:
   stage: pretest
-  except:
-    variables:
-      - $ENABLE_NIGHTLY_BUILDS
-  image: i10git.cs.fau.de:5005/pycodegen/pycodegen/full
+  extends: .every-commit
+  image: i10git.cs.fau.de:5005/pycodegen/pycodegen/full:cupy12.3
   script:
     # - pip install sympy --upgrade
     - export NUM_CORES=$(nproc --all)
@@ -22,7 +39,7 @@ tests-and-coverage:
     - pip install git+https://gitlab-ci-token:${CI_JOB_TOKEN}@i10git.cs.fau.de/pycodegen/pystencils.git@master#egg=pystencils
     - env
     - pip list
-    - py.test -v -n $NUM_CORES --cov-report html --cov-report term --cov=. -m "not longrun" --junitxml=report.xml
+    - py.test -v -n $NUM_CORES --cov-report html --cov-report xml --cov-report term --cov=. -m "not longrun" --junitxml=report.xml
     - python3 -m coverage xml
   tags:
     - docker
@@ -62,25 +79,22 @@ tests-and-coverage-with-longrun:
 
 minimal-conda:
   stage: pretest
-  except:
-    variables:
-      - $ENABLE_NIGHTLY_BUILDS
+  extends: .every-commit
   image: i10git.cs.fau.de:5005/pycodegen/pycodegen/minimal_conda
   script:
     - pip install git+https://gitlab-ci-token:${CI_JOB_TOKEN}@i10git.cs.fau.de/pycodegen/pystencils.git@master#egg=pystencils
-    - python setup.py quicktest
+    - pip install -e .
+    - python quicktest.py
   tags:
     - docker
 
 # Linter for code formatting
 flake8-lint:
   stage: pretest
-  except:
-    variables:
-      - $ENABLE_NIGHTLY_BUILDS
+  extends: .every-commit
   image: i10git.cs.fau.de:5005/pycodegen/pycodegen/full
   script:
-    - flake8 lbmpy
+    - flake8 src/lbmpy
   tags:
     - docker
     - cuda11
@@ -90,9 +104,7 @@ flake8-lint:
 # pipeline with latest python version
 latest-python:
   stage: test
-  except:
-    variables:
-      - $ENABLE_NIGHTLY_BUILDS
+  extends: .every-commit
   image: i10git.cs.fau.de:5005/pycodegen/pycodegen/latest_python
   before_script:
     - pip install git+https://gitlab-ci-token:${CI_JOB_TOKEN}@i10git.cs.fau.de/pycodegen/pystencils.git@master#egg=pystencils
@@ -113,34 +125,34 @@ latest-python:
       junit: report.xml
 
 # Minimal tests in windows environment
-minimal-windows:
-  stage: test
-  except:
-    variables:
-      - $ENABLE_NIGHTLY_BUILDS
-  tags:
-    - win
-  script:
-    - export NUM_CORES=$(nproc --all)
-    - export MPLBACKEND=Agg
-    - source /cygdrive/c/Users/build/Miniconda3/Scripts/activate
-    - source activate pystencils
-    - pip install git+https://gitlab-ci-token:${CI_JOB_TOKEN}@i10git.cs.fau.de/pycodegen/pystencils.git@master#egg=pystencils
-    - python -c "import numpy"
-    - pip install sympy==1.9
-    - py.test -v -m "not (notebook or longrun)"
+#minimal-windows:
+#  stage: test
+#  except:
+#    variables:
+#      - $ENABLE_NIGHTLY_BUILDS
+#  tags:
+#    - win
+#  script:
+#    - export NUM_CORES=$(nproc --all)
+#    - export MPLBACKEND=Agg
+#    - source /cygdrive/c/Users/build/Miniconda3/Scripts/activate
+#    - source activate pystencils
+#    - pip install git+https://gitlab-ci-token:${CI_JOB_TOKEN}@i10git.cs.fau.de/pycodegen/pystencils.git@master#egg=pystencils
+#    - python -c "import numpy"
+#    - pip install sympy==1.9
+#    - py.test -v -m "not (notebook or longrun)"
 
 minimal-sympy-master:
   stage: test
-  except:
-    variables:
-      - $ENABLE_NIGHTLY_BUILDS
+  extends: .every-commit
   image: i10git.cs.fau.de:5005/pycodegen/pycodegen/minimal_conda
+  before_script:
+    - pip install -e .
   script:
     - pip install git+https://gitlab-ci-token:${CI_JOB_TOKEN}@i10git.cs.fau.de/pycodegen/pystencils.git@master#egg=pystencils
     - python -m pip install --upgrade git+https://github.com/sympy/sympy.git
     - pip list
-    - python setup.py quicktest
+    - python quicktest.py
   allow_failure: true
   tags:
     - docker
@@ -148,9 +160,7 @@ minimal-sympy-master:
 
 ubuntu:
   stage: test
-  except:
-    variables:
-      - $ENABLE_NIGHTLY_BUILDS
+  extends: .every-commit
   image: i10git.cs.fau.de:5005/pycodegen/pycodegen/ubuntu
   before_script:
     # - apt-get -y remove python3-sympy
@@ -163,7 +173,7 @@ ubuntu:
     - echo "backend:template" > ~/.config/matplotlib/matplotlibrc
     - env
     - pip3 list
-    - pytest-3 -v -n $NUM_CORES -m "not longrun" --junitxml=report.xml
+    - pytest -v -n $NUM_CORES -m "not longrun" --junitxml=report.xml
   tags:
     - docker
     - cuda11
@@ -207,11 +217,44 @@ pycodegen-integration:
     - cuda11
     - AVX
 
+# -------------------- Scheduled Tasks --------------------------------------------------------------------------
+
+
+nightly-sympy:
+  stage: nightly
+  extends: .scheduled
+  image: i10git.cs.fau.de:5005/pycodegen/pycodegen/latest_python
+  before_script:
+    - pip install -e .
+    - pip install git+https://gitlab-ci-token:${CI_JOB_TOKEN}@i10git.cs.fau.de/pycodegen/pystencils.git@master#egg=pystencils
+    - pip install --upgrade --pre sympy
+  script:
+    - env
+    - pip list
+    - export NUM_CORES=$(nproc --all)
+    - mkdir -p ~/.config/matplotlib
+    - echo "backend:template" > ~/.config/matplotlib/matplotlibrc
+    - mkdir public
+    - pytest -v -n $NUM_CORES -m "not longrun" --junitxml=report.xml
+  tags:
+    - docker
+    - AVX
+    - cuda
+  artifacts:
+    when: always
+    reports:
+      junit: report.xml
+
+
 # -------------------- Documentation and deploy ------------------------------------------------------------------------
 
 build-documentation:
-  stage: test
+  stage: docs
+  needs: []
+  extends: .every-commit
   image: i10git.cs.fau.de:5005/pycodegen/pycodegen/documentation
+  before_script:
+    - pip install -e .
   script:
     - export PYTHONPATH=`pwd`
     - pip install git+https://gitlab-ci-token:${CI_JOB_TOKEN}@i10git.cs.fau.de/pycodegen/pystencils.git@master#egg=pystencils
@@ -227,7 +270,9 @@ build-documentation:
 
 pages:
   image: i10git.cs.fau.de:5005/pycodegen/pycodegen/full
+  extends: .every-commit-master
   stage: deploy
+  needs: ["tests-and-coverage", "build-documentation"]
   script:
     - ls -l
     - mv coverage_report html_doc
@@ -237,5 +282,3 @@ pages:
       - public
   tags:
     - docker
-  only:
-    - master@pycodegen/lbmpy

COPYING.txt

-------------------------   Important ---------------------------------
-
-lbmpy is under the following GNU AGPLv3 license. 
-This license holds for the sources of lbmpy itself as well 
-as for all kernels generated with lbmpy i.e. 
-the output of lbmpy is also protected by the GNU AGPLv3 license. 
-
-----------------------------------------------------------------------
-
-
-
-                    
                     GNU AFFERO GENERAL PUBLIC LICENSE
                        Version 3, 19 November 2007
 

MANIFEST.in

-include README.md
-include COPYING.txt
 include AUTHORS.txt
 include CONTRIBUTING.md
-global-include *.pyx
-include versioneer.py
-include lbmpy/_version.py
+include CHANGELOG.md

README.md

@@ -71,6 +71,7 @@ Many thanks go to the [contributors](https://i10git.cs.fau.de/pycodegen/lbmpy/-/
 If you use lbmpy in a publication, please cite the following articles:
 
 Overview:
+  - F. Hennig et al, Advanced Automatic Code Generation for Multiple Relaxation-Time Lattice Boltzmann Methods. SIAM Journal on Scientific Computing, 2023. https://doi.org/10.1137/22M1531348 ([Preprint](https://arxiv.org/abs/2211.02435))
   - M. Bauer et al, lbmpy: Automatic code generation for efficient parallel lattice Boltzmann methods. Journal of Computational Science, 2021. https://doi.org/10.1016/j.jocs.2020.101269 ([Preprint](https://arxiv.org/abs/2001.11806))
 
 Multiphase:

binder/environment.yml

@@ -7,7 +7,7 @@
 #     conda env create -f conda_environment_user.yml
 #     . activate pystencils
 #
-# If you have CUDA installed and want to use your GPU, uncomment the last line to install pycuda
+# If you have CUDA or ROCm installed and want to use your GPU, uncomment the last line to install cupy
 #
 # ----------------------------------------------------------------------------------------------------------------------
 
@@ -33,4 +33,4 @@ dependencies:
       - pyevtk # VTK output for serial simulations
       - blitzdb # file-based No-SQL database to store simulation results
       - pystencils
-      #- pycuda # add this if you have CUDA installed
+      #- cupy # add this if you have CUDA or ROCm installed

conftest.py

@@ -19,9 +19,10 @@ try:
     import pyximport
 
     pyximport.install(language_level=3)
+
+    from lbmpy.phasefield.simplex_projection import simplex_projection_2d  # NOQA
 except ImportError:
     pass
-from lbmpy.phasefield.simplex_projection import simplex_projection_2d  # NOQA
 
 SCRIPT_FOLDER = os.path.dirname(os.path.realpath(__file__))
 sys.path.insert(0, os.path.abspath('lbmpy'))
@@ -42,33 +43,35 @@ def add_path_to_ignore(path):
 
 collect_ignore = [os.path.join(SCRIPT_FOLDER, "doc", "conf.py"),
                   os.path.join(SCRIPT_FOLDER, "doc", "img", "mb_discretization", "maxwell_boltzmann_stencil_plot.py")]
-add_path_to_ignore('pystencils_tests/benchmark')
 add_path_to_ignore('_local_tmp')
 
 try:
-    import pycuda
+    import cupy
 except ImportError:
-    collect_ignore += [os.path.join(SCRIPT_FOLDER, "lbmpy_tests/test_cpu_gpu_equivalence.py")]
+    collect_ignore += [os.path.join(SCRIPT_FOLDER, "tests/test_cpu_gpu_equivalence.py")]
 
 try:
     import waLBerla
 except ImportError:
-    collect_ignore += [os.path.join(SCRIPT_FOLDER, "lbmpy_tests/test_datahandling_parallel.py")]
+    collect_ignore += [os.path.join(SCRIPT_FOLDER, "tests/test_datahandling_parallel.py")]
 
 try:
     import blitzdb
 except ImportError:
-    collect_ignore += [os.path.join(SCRIPT_FOLDER, "lbmpy_tests/benchmark"),
+    collect_ignore += [os.path.join(SCRIPT_FOLDER, "tests/benchmark"),
                        os.path.join(SCRIPT_FOLDER,
-                                    "lbmpy_tests/full_scenarios/kida_vortex_flow/scenario_kida_vortex_flow.py")]
+                                    "tests/full_scenarios/kida_vortex_flow/scenario_kida_vortex_flow.py"),
+                       os.path.join(SCRIPT_FOLDER, "tests/full_scenarios/shear_wave/scenario_shear_wave.py"),
+                       os.path.join(SCRIPT_FOLDER, "tests/test_json_serializer.py"),
+                       os.path.join(SCRIPT_FOLDER, "src/lbmpy/db.py")]
 
 if platform.system().lower() == 'windows':
-    collect_ignore += [os.path.join(SCRIPT_FOLDER, "lbmpy_tests/test_quicktests.py")]
+    collect_ignore += [os.path.join(SCRIPT_FOLDER, "tests/test_quicktests.py")]
 
 sver = sympy.__version__.split(".")
 if int(sver[0]) == 1 and int(sver[1]) < 2:
-    add_path_to_ignore('lbmpy_tests/phasefield')
-    collect_ignore += [os.path.join(SCRIPT_FOLDER, "lbmpy_tests/test_n_phase_boyer_noncoupled.ipynb")]
+    add_path_to_ignore('tests/phasefield')
+    collect_ignore += [os.path.join(SCRIPT_FOLDER, "tests/test_n_phase_boyer_noncoupled.ipynb")]
 
 collect_ignore += [os.path.join(SCRIPT_FOLDER, 'setup.py')]
 
@@ -104,18 +107,25 @@ class IPyNbTest(pytest.Item):
 
         # disable matplotlib output
         exec("import matplotlib.pyplot as p; "
+             "p.close('all'); "
              "p.switch_backend('Template')", global_dict)
 
         # in notebooks there is an implicit plt.show() - if this is not called a warning is shown when the next
         # plot is created. This warning is suppressed here
+        # Also animations cannot be shown, which also leads to a warning.
         exec("import warnings;"
-             "warnings.filterwarnings('ignore', 'Adding an axes using the same arguments as a previous.*');",
+             "warnings.filterwarnings('ignore', 'Adding an axes using the same arguments as a previous.*');"
+             "warnings.filterwarnings('ignore', 'Animation was deleted without rendering anything.*');",
              global_dict)
         with tempfile.NamedTemporaryFile() as f:
             f.write(self.code.encode())
             f.flush()
             runpy.run_path(f.name, init_globals=global_dict, run_name=self.name)
 
+        #   Close any open figures
+        exec("import matplotlib.pyplot as p; "
+             "p.close('all')", global_dict)
+
 
 class IPyNbFile(pytest.File):
     def collect(self):
@@ -138,10 +148,19 @@ class IPyNbFile(pytest.File):
         pass
 
 
-def pytest_collect_file(path, parent):
-    glob_exprs = ["*demo*.ipynb", "*tutorial*.ipynb", "test_*.ipynb"]
-    if any(path.fnmatch(g) for g in glob_exprs):
-        if pytest_version >= 50403:
-            return IPyNbFile.from_parent(fspath=path, parent=parent)
-        else:
-            return IPyNbFile(path, parent)
+if pytest_version >= 70000:
+    #   Since pytest 7.0, usage of `py.path.local` is deprecated and `pathlib.Path` should be used instead
+    import pathlib
+
+    def pytest_collect_file(file_path: pathlib.Path, parent):
+        glob_exprs = ["*demo*.ipynb", "*tutorial*.ipynb", "test_*.ipynb"]
+        if any(file_path.match(g) for g in glob_exprs):
+            return IPyNbFile.from_parent(path=file_path, parent=parent)
+else:
+    def pytest_collect_file(path, parent):
+        glob_exprs = ["*demo*.ipynb", "*tutorial*.ipynb", "test_*.ipynb"]
+        if any(path.fnmatch(g) for g in glob_exprs):
+            if pytest_version >= 50403:
+                return IPyNbFile.from_parent(fspath=path, parent=parent)
+            else:
+                return IPyNbFile(path, parent)

doc/conf.py

@@ -33,7 +33,7 @@ version = re.sub(r'(\d+\.\d+)\.\d+(.*)', r'\1\2', lbmpy.__version__)
 version = re.sub(r'(\.dev\d+).*?$', r'\1', version)
 # The full version, including alpha/beta/rc tags.
 release = lbmpy.__version__
-language = None
+language = 'en'
 exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store', '**.ipynb_checkpoints']
 default_role = 'any'
 pygments_style = 'sphinx'

doc/index.rst

@@ -6,6 +6,9 @@ lbmpy
     :maxdepth: 2
 
     sphinx/tutorials.rst
+    sphinx/methods.rst
+    sphinx/boundary_conditions.rst
+    sphinx/forcemodels.rst
     sphinx/api.rst
 
 

doc/notebooks/01_tutorial_predefinedScenarios.ipynb

@@ -8,7 +8,7 @@
     {
      "data": {
       "text/plain": [
-       "<module 'pycuda' from '/home/markus/miniconda3/envs/pystencils/lib/python3.8/site-packages/pycuda/__init__.py'>"
+       "<module 'cupy' from '/home/markus/.local/lib/python3.11/site-packages/cupy/__init__.py'>"
       ]
      },
      "execution_count": 1,
@@ -18,7 +18,7 @@
    ],
    "source": [
     "import pytest\n",
-    "pytest.importorskip('pycuda')"
+    "pytest.importorskip('cupy')"
    ]
   },
   {
@@ -660,7 +660,7 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python 3",
+   "display_name": "Python 3 (ipykernel)",
    "language": "python",
    "name": "python3"
   },
@@ -674,7 +674,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.8.2"
+   "version": "3.11.0rc1"
   }
  },
  "nbformat": 4,

doc/notebooks/04_tutorial_cumulant_LBM.ipynb

@@ -673,7 +673,7 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python 3",
+   "display_name": "Python 3 (ipykernel)",
    "language": "python",
    "name": "python3"
   },
@@ -687,7 +687,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.8.2"
+   "version": "3.11.4"
   },
   "vscode": {
    "interpreter": {

doc/notebooks/06_tutorial_modifying_method_smagorinsky.ipynb

 %% Cell type:code id: tags:
 ``` python
 from lbmpy.session import *
 from lbmpy.relaxationrates import *
 ```
 %% Cell type:markdown id: tags:
 # Tutorial 06: Modifying a LBM method: Smagorinsky model
 In this demo, we show how to modify a lattice Boltzmann method. As example we are going to add a simple turbulence model, by introducing a rule that locally computes the relaxation parameter dependent on the local strain rate tensor. The Smagorinsky model is implemented directly in *lbmpy* as well, however here we take the manual approach to demonstrate how a LB method can be changed in *lbmpy*.
 ## 1) Theoretical background
 Since we have *sympy* available, we want to start out with the basic model equations and derive the concrete equations ourselves. This approach is less error prone, since the calculations are done by the computer algebra system, and oftentimes this approach is also more general and easier to understand.
 ### a) Smagorinsky model
 The basic idea of the Smagorinsky turbulence model is to safe compute time, by not resolving the smallest eddies of the flow on the grid, but model them by an artifical dissipation term.
 The energy dissipation of small scale vortices is taken into account by introducing a "turbulent viscosity". This additional viscosity depends on local flow properties, namely the local shear rates. The larger the local shear rates the higher the turbulent viscosity and the more artifical dissipation is added.
 The total viscosity is
 $$\nu_{total} = \nu_0 + \underbrace{(C_S \Delta)^2 |S|}_{\nu_{t}}$$
 where $\nu_0$ is the normal viscosity, $C_S$ is the Smagorinsky constant, not to be confused with the speed of sound! Typical values of the Smagorinsky constant are between 0.1 - 0.2. The filter length $\Delta$ is chosen as 1 in lattice coordinates.
 The quantity $|S|$ is computed from the local strain rate tensor $S$ that is given by
 $$S_{ij} = \frac{1}{2} \left( \partial_i u_j + \partial_j u_i \right)$$
 and
 $$|S| = \sqrt{2 S_{ij} S_{ij}}$$
 ### b) LBM implementation of Smagorinsky model
 To add the Smagorinsky model to a LB scheme one has to first compute the strain rate tensor $S_{ij}$ in each cell, and compute the turbulent viscosity $\nu_t$ from it. Then the local relaxation rate has to be adapted to match the total viscosity $\nu_{total}$ instead of the standard viscosity $\nu_0$.
 A fortunate property of LB methods is, that the strain rate tensor can be computed locally from the non-equilibrium part of the distribution function. This is somewhat surprising, since the strain rate tensor contains first order derivatives. The strain rate tensor can be obtained by
 $$S_{ij} = - \frac{3 \omega_s}{2 \rho_{(0)}} \Pi_{ij}^{(neq)}$$
 where $\omega_s$ is the relaxation rate that determines the viscosity, $\rho_{(0)}$ is $\rho$ in compressible models and $1$ for incompressible schemes.
 $\Pi_{ij}^{(neq)}$ is the second order moment tensor of the non-equilibrium part of the distribution functions $f^{(neq)} = f - f^{(eq)}$ and can be computed as
 $$\Pi_{ij}^{(neq)} = \sum_q c_{qi} c_{qj} \; f_q^{(neq)}$$
 %% Cell type:markdown id: tags:
 We first have to find a closed form for $S_{ij}$ since in the formula above, it depends on $\omega$, which should be adapated according to $S_{ij}$.
 So we compute $\omega$ and insert it into the formula for $S$:
 %% Cell type:code id: tags:
 ``` python
 τ_0, ρ, ω, ω_total, ω_0 = sp.symbols("tau_0 rho omega omega_total omega_0", positive=True, real=True)
 ν_0, C_S, S, Π = sp.symbols("nu_0, C_S, |S|, Pi", positive=True, real=True)
 Seq = sp.Eq(S, 3 * ω / 2 * Π)
 Seq
 ```
 %% Output
     $\displaystyle |S| = \frac{3 \Pi \omega}{2}$
           3⋅Π⋅ω
     |S| = ─────
             2
 %% Cell type:markdown id: tags:
 Note that we left of the minus, since we took the absolute value of both tensor. The absolute value is defined as above, with the factor of two inside the square root. The $\rho_{(0)}$ has been left out, remembering that $\Pi^{(neq)}$ has to be divided by $\rho$ in case of compressible models|.
 Next, we compute $\omega$ from the total viscosity as given by the Smagorinsky equation:
 %% Cell type:code id: tags:
 ``` python
 relaxation_rate_from_lattice_viscosity(ν_0 + C_S ** 2 * S)
 ```
 %% Output
     $\displaystyle \frac{2}{6 C_{S}^{2} |S| + 6 \nu_{0} + 1}$
               2
     ─────────────────────
          2
     6⋅C_S ⋅|S| + 6⋅ν₀ + 1
 %% Cell type:markdown id: tags:
 and insert it into the equation for $|S|$
 %% Cell type:code id: tags:
 ``` python
 Seq2 = Seq.subs(ω, relaxation_rate_from_lattice_viscosity(ν_0 + C_S **2 * S ))
 Seq2
 ```
 %% Output
     $\displaystyle |S| = \frac{3 \Pi}{6 C_{S}^{2} |S| + 6 \nu_{0} + 1}$
                    3⋅Π
     |S| = ─────────────────────
                2
           6⋅C_S ⋅|S| + 6⋅ν₀ + 1
 %% Cell type:markdown id: tags:
 This equation contains only known quantities, such that we can solve it for $|S|$.
 Additionally we substitute the lattice viscosity $\nu_0$ by the original relaxation time $\tau_0$. The resulting equations get simpler using relaxation times instead of rates.
 %% Cell type:code id: tags:
 ``` python
 solveRes = sp.solve(Seq2, S)
 assert len(solveRes) == 1
 SVal = solveRes[0]
 SVal = SVal.subs(ν_0, lattice_viscosity_from_relaxation_rate(1 / τ_0)).expand()
 SVal
 ```
 %% Output
     $\displaystyle - \frac{\tau_{0}}{6 C_{S}^{2}} + \frac{\sqrt{72 C_{S}^{2} \Pi + 4 \tau_{0}^{2}}}{12 C_{S}^{2}}$
                   ___________________
                  ╱       2         2
         τ₀     ╲╱  72⋅C_S ⋅Π + 4⋅τ₀
     - ────── + ──────────────────────
            2                2
       6⋅C_S           12⋅C_S
 %% Cell type:markdown id: tags:
 Knowning $|S|$ we can compute the total relaxation time using
 $$\nu_{total} = \nu_0 +C_S^2 |S|$$
 %% Cell type:code id: tags:
 ``` python
 τ_val = 1 / (relaxation_rate_from_lattice_viscosity(lattice_viscosity_from_relaxation_rate(1/τ_0) + C_S**2 * SVal)).cancel()
 τ_val
 ```
 %% Output
     $\displaystyle \frac{\tau_{0}}{2} + \frac{\sqrt{18 C_{S}^{2} \Pi + \tau_{0}^{2}}}{2}$
             _________________
            ╱       2       2
     τ₀   ╲╱  18⋅C_S ⋅Π + τ₀
     ── + ────────────────────
     2             2
 %% Cell type:markdown id: tags:
 To compute $\Pi^{(neq)}$ we use the following functions:
 %% Cell type:code id: tags:
 ``` python
 def second_order_moment_tensor(function_values, stencil):
     assert len(function_values) == len(stencil)
     dim = len(stencil[0])
     return sp.Matrix(dim, dim, lambda i, j: sum(c[i] * c[j] * f for f, c in zip(function_values, stencil)))
 def frobenius_norm(matrix, factor=1):
     return sp.sqrt(sum(i*i for i in matrix) * factor)
 ```
 %% Cell type:markdown id: tags:
 In the next cell we construct equations that take an standard relaxation rate $\omega_0$ and compute a new relaxation rate $\omega_{total}$ according to the Smagorinksy model, using `τ_val` computed above
 %% Cell type:code id: tags:
 ``` python
 def smagorinsky_equations(ω_0, ω_total, method):
     f_neq = sp.Matrix(method.pre_collision_pdf_symbols) - method.get_equilibrium_terms()
     return [sp.Eq(τ_0, 1 / ω_0),
             sp.Eq(Π, frobenius_norm(second_order_moment_tensor(f_neq, method.stencil), factor=2)),
             sp.Eq(ω_total, 1 / τ_val)]
 smagorinsky_equations(ω_0, ω_total, create_lb_method())
 ```
 %% Output
     $\displaystyle \left[ \tau_{0} = \frac{1}{\omega_{0}}, \  \Pi = \sqrt{4 \left(- f_{5} + f_{6} + f_{7} - f_{8} - u_{0} u_{1}\right)^{2} + 2 \left(- \frac{\delta_{\rho}}{3} + f_{1} + f_{2} + f_{5} + f_{6} + f_{7} + f_{8} - u_{1}^{2}\right)^{2} + 2 \left(- \frac{\delta_{\rho}}{3} + f_{3} + f_{4} + f_{5} + f_{6} + f_{7} + f_{8} - u_{0}^{2}\right)^{2}}, \  \omega_{total} = \frac{1}{\frac{\tau_{0}}{2} + \frac{\sqrt{18 C_{S}^{2} \Pi + \tau_{0}^{2}}}{2}}\right]$
     ⎡                  ___________________________________________________________
     ⎢                 ╱
     ⎢     1          ╱                                2     ⎛  δᵨ
     ⎢τ₀ = ──, Π =   ╱   4⋅(-f₅ + f₆ + f₇ - f₈ - u₀⋅u₁)  + 2⋅⎜- ── + f₁ + f₂ + f₅ +
     ⎢     ω₀      ╲╱                                        ⎝  3
     ⎢
     ⎢
     ⎢
     ⎣
     
     ______________________________________________________________________
                         2                                               2
                       2⎞      ⎛  δᵨ                                   2⎞
      f₆ + f₇ + f₈ - u₁ ⎟  + 2⋅⎜- ── + f₃ + f₄ + f₅ + f₆ + f₇ + f₈ - u₀ ⎟  , ωₜₒₜₐₗ
                        ⎠      ⎝  3                                     ⎠
     
     
     
     
     
                                 ⎤
                                 ⎥
                    1            ⎥
      = ─────────────────────────⎥
                _________________⎥
               ╱       2       2 ⎥
        τ₀   ╲╱  18⋅C_S ⋅Π + τ₀  ⎥
        ── + ────────────────────⎥
        2             2          ⎦
 %% Cell type:markdown id: tags:
 ## 2) Application: Channel flow
 Next we modify a *lbmpy* scenario to use the Smagorinsky model.
 We create a MRT method, where we fix all relaxation rates except the relaxation rate that controls the viscosity.
 %% Cell type:code id: tags:
 ``` python
-lbm_conifg = LBMConfig(stencil=Stencil.D2Q9, method=Method.MRT, force=(1e-6, 0),
+lbm_config = LBMConfig(stencil=Stencil.D2Q9, method=Method.MRT, force=(1e-6, 0),
                        force_model=ForceModel.LUO, relaxation_rates=[ω, 1.9, 1.9, 1.9])
-method = create_lb_method(lbm_config=lbm_conifg)
+method = create_lb_method(lbm_config=lbm_config)
 method
 ```
 %% Output
     <lbmpy.methods.momentbased.momentbasedmethod.MomentBasedLbMethod at 0x7f745d5c3b20>
 %% Cell type:markdown id: tags:
 Only the collision rule has to be changed. Thus we first construct the collision rule, add the Smagorinsky equations and create a normal scenario from the modified collision rule. To avoid that the macroscopic quantity symbols in the Smagorinsky equations fall prey to optimization, we must disable simplification:
 %% Cell type:code id: tags:
 ``` python
 optimization = {'simplification' : False}
 collision_rule = create_lb_collision_rule(lb_method=method, optimization=optimization)
 collision_rule = collision_rule.new_with_substitutions({ω: ω_total})
 collision_rule.subexpressions += smagorinsky_equations(ω, ω_total, method)
 collision_rule.topological_sort(sort_subexpressions=True, sort_main_assignments=False)
 collision_rule
 ```
 %% Output
     AssignmentCollection: d_6, d_5, d_2, d_3, d_0, d_1, d_7, d_4, d_8 <- f(f_2, f_4, f_7, f_5, omega_total, f_6, f_3, f_1, f_0, f_8)
 %% Cell type:markdown id: tags:
 In the next cell the collision rule is simplified by extracting common subexpressions
 %% Cell type:code id: tags:
 ``` python
 from pystencils.simp import sympy_cse
 #collision_rule = sympy_cse(collision_rule)
 ```
 %% Cell type:markdown id: tags:
 A channel scenario can be created from a modified collision rule:
 %% Cell type:code id: tags:
 ``` python
 ch = create_channel((300, 100), force=1e-6, collision_rule=collision_rule,
                     kernel_params={"C_S": 0.12, "omega": 1.999})
 ```
 %% Cell type:code id: tags:
 ``` python
 #show_code(ch.ast)
 ```
 %% Cell type:code id: tags:
 ``` python
 ch.run(5000)
 ```
 %% Cell type:code id: tags:
 ``` python
 plt.figure(dpi=200)
 plt.vector_field(ch.velocity[:, :])
 np.max(ch.velocity[:, :])
 ```
 %% Output
     $\displaystyle 0.00504266401703371$
     0.00504266401703371
 %% Cell type:markdown id: tags:
 ## Appendix: Strain rate tensor formula from Chapman Enskog
 The connection between $S_{ij}$ and $\Pi_{ij}^{(neq)}$ can be seen using a Chapman Enskog expansion. Since *lbmpy* has a module that automatically does this expansions we can have a look at it:
 %% Cell type:code id: tags:
 ``` python
 from lbmpy.chapman_enskog import ChapmanEnskogAnalysis, CeMoment
 from lbmpy.chapman_enskog.chapman_enskog import remove_higher_order_u
 compressible_model = create_lb_method(stencil=Stencil.D2Q9, compressible=True, zero_centered=False)
 incompressible_model = create_lb_method(stencil=Stencil.D2Q9, compressible=False, zero_centered=False)
 ce_compressible = ChapmanEnskogAnalysis(compressible_model)
 ce_incompressible = ChapmanEnskogAnalysis(incompressible_model)
 ```
 %% Cell type:markdown id: tags:
 The Chapman Enskog analysis yields expresssions for the moment
 $\Pi = \Pi^{(eq)} + \epsilon \Pi^{(1)} +  \epsilon^2 \Pi^{(2)} \cdots$
 and the strain rate tensor is related to $\Pi^{(1)}$. However the best approximation we have for $\Pi^{(1)}$ is
 $\Pi^{(neq)}$. For details, see the paper "Shear stress in lattice Boltzmann simulations" by Krüger, Varnik and Raabe from 2009.
 Lets look at the values of $\Pi^{(1)}$ obtained from the Chapman enskog expansion:
 %% Cell type:code id: tags:
 ``` python
 Π_1_xy = CeMoment("\\Pi", moment_tuple=(1,1), superscript=1)
 Π_1_xx = CeMoment("\\Pi", moment_tuple=(2,0), superscript=1)
 Π_1_yy = CeMoment("\\Pi", moment_tuple=(0,2), superscript=1)
 components = (Π_1_xx, Π_1_yy, Π_1_xy)
 Π_1_xy_val = ce_compressible.higher_order_moments[Π_1_xy]
 Π_1_xy_val
 ```
 %% Output
     $\displaystyle \frac{\rho u_{0}^{2} {\partial^{(1)}_{0} u_{1}} + 2 \rho u_{0} u_{1} {\partial^{(1)}_{0} u_{0}} + 2 \rho u_{0} u_{1} {\partial^{(1)}_{1} u_{1}} + \rho u_{1}^{2} {\partial^{(1)}_{1} u_{0}} - \frac{\rho {\partial^{(1)}_{1} u_{0}}}{3} - \frac{\rho {\partial^{(1)}_{0} u_{1}}}{3} + u_{0}^{2} u_{1} {\partial^{(1)}_{0} \rho} + u_{0} u_{1}^{2} {\partial^{(1)}_{1} \rho}}{\omega}$
         2                                                    2          ρ⋅D(u_0)
     ρ⋅u₀ ⋅D(u_1) + 2⋅ρ⋅u₀⋅u₁⋅D(u_0) + 2⋅ρ⋅u₀⋅u₁⋅D(u_1) + ρ⋅u₁ ⋅D(u_0) - ──────── -
                                                                            3
     ──────────────────────────────────────────────────────────────────────────────
                                                                ω
     
      ρ⋅D(u_1)     2                  2
      ──────── + u₀ ⋅u₁⋅D(rho) + u₀⋅u₁ ⋅D(rho)
         3
     ─────────────────────────────────────────
     
 %% Cell type:markdown id: tags:
 This term has lots of higher order error terms in it. We assume that $u$ is small in lattice coordinates, so if we neglect all terms in $u$ that are quadratic or higher we get:
 %% Cell type:code id: tags:
 ``` python
 remove_higher_order_u(Π_1_xy_val.expand())
 ```
 %% Output
     $\displaystyle - \frac{\rho {\partial^{(1)}_{1} u_{0}}}{3 \omega} - \frac{\rho {\partial^{(1)}_{0} u_{1}}}{3 \omega}$
       ρ⋅D(u_0)   ρ⋅D(u_1)
     - ──────── - ────────
         3⋅ω        3⋅ω
 %% Cell type:markdown id: tags:
 Putting these steps together into a function, we can display them for the different cases quickly:
 %% Cell type:code id: tags:
 ``` python
 def get_Π_1(ce_analysis, component):
     val = ce_analysis.higher_order_moments[component]
     return remove_higher_order_u(val.expand())
 ```
 %% Cell type:markdown id: tags:
 Compressible case:
 %% Cell type:code id: tags:
 ``` python
 tuple(get_Π_1(ce_compressible, Pi) for Pi in components)
 ```
 %% Output
     $\displaystyle \left( - \frac{2 \rho {\partial^{(1)}_{0} u_{0}}}{3 \omega}, \  - \frac{2 \rho {\partial^{(1)}_{1} u_{1}}}{3 \omega}, \  - \frac{\rho {\partial^{(1)}_{1} u_{0}}}{3 \omega} - \frac{\rho {\partial^{(1)}_{0} u_{1}}}{3 \omega}\right)$
     ⎛-2⋅ρ⋅D(u_0)   -2⋅ρ⋅D(u_1)     ρ⋅D(u_0)   ρ⋅D(u_1)⎞
     ⎜────────────, ────────────, - ──────── - ────────⎟
     ⎝    3⋅ω           3⋅ω           3⋅ω        3⋅ω   ⎠
 %% Cell type:markdown id: tags:
 Incompressible case:
 %% Cell type:code id: tags:
 ``` python
 tuple(get_Π_1(ce_incompressible, Pi) for Pi in components)
 ```
 %% Output
     $\displaystyle \left( \frac{2 u_{0} {\partial^{(1)}_{0} \rho}}{3 \omega} - \frac{2 {\partial^{(1)}_{0} u_{0}}}{3 \omega}, \  \frac{2 u_{1} {\partial^{(1)}_{1} \rho}}{3 \omega} - \frac{2 {\partial^{(1)}_{1} u_{1}}}{3 \omega}, \  \frac{u_{0} {\partial^{(1)}_{1} \rho}}{3 \omega} + \frac{u_{1} {\partial^{(1)}_{0} \rho}}{3 \omega} - \frac{{\partial^{(1)}_{1} u_{0}}}{3 \omega} - \frac{{\partial^{(1)}_{0} u_{1}}}{3 \omega}\right)$
     ⎛2⋅u₀⋅D(rho)   2⋅D(u_0)  2⋅u₁⋅D(rho)   2⋅D(u_1)  u₀⋅D(rho)   u₁⋅D(rho)   D(u_0
     ⎜─────────── - ────────, ─────────── - ────────, ───────── + ───────── - ─────
     ⎝    3⋅ω         3⋅ω         3⋅ω         3⋅ω        3⋅ω         3⋅ω       3⋅ω
     
     )   D(u_1)⎞
     ─ - ──────⎟
          3⋅ω  ⎠
 %% Cell type:markdown id: tags:
 In the incompressible case has some terms $\partial \rho$ which are zero, since $\rho$ is assumed constant.
 Leaving out the error terms we finally obtain:
 $$\Pi_{ij}^{(neq)} \approx \Pi_{ij}^{(1)} = -\frac{2 \rho_{(0)}}{3 \omega_s} \left( \partial_i u_j + \partial_j u_i \right)$$