minor cleanup
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@ -68,7 +68,7 @@ naturally transfers to including $\nu$ as a degree of freedom.
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As $\mathbf{u}$ is typically a vector-valued function, $\partial \mathcal P_i / \partial \mathbf{u}$ denotes
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a Jacobian matrix $J$ rather than a single value:
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% test
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%
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$$ \begin{aligned}
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\frac{ \partial \mathcal P_i }{ \partial \mathbf{u} } =
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\begin{bmatrix}
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@ -83,6 +83,7 @@ $$ \begin{aligned}
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\partial \mathcal P_{i,d} / \partial u_{d}
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\end{bmatrix}
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\end{aligned} $$
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%
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where, as above, $d$ denotes the number of components in $\mathbf{u}$. As $\mathcal P$ maps one value of
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$\mathbf{u}$ to another, the jacobian is square and symmetric here. Of course this isn't necessarily the case
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for general model equations, but non-square Jacobian matrices would not cause any problems for differentiable
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@ -139,12 +140,10 @@ state of the forward evaluation for backpropagation (the "$g(x)$" above). For a
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simulation, however, we're not overly interested in every single intermediate result our solver produces.
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Typically, we're more concerned with significant updates such as the step from $\mathbf{u}(t)$ to $\mathbf{u}(t+\Delta t)$.
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%provide discretized simulator of physical phenomenon as differentiable operator.
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Thus, in practice it is a very good idea to break down the solving process into a sequence
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of meaningful but _monolithic_ operators. This not only saves a lot of work by preventing the calculation
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of unnecessary intermediate results, it also allows us to choose the best possible numerical methods
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to compute the updates (and derivatives) for these operators.
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%in practice break down into larger, monolithic components
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E.g., as this process is very similar to adjoint method optimizations, we can re-use many of the techniques
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that were developed in this field, or leverage established numerical methods. E.g.,
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we could leverage the $O(n)$ runtime of multigrid solvers for matrix inversion.
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@ -10,11 +10,10 @@ implementations for each of them.
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More specifically, we will look at:
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* Time series predictions, i.e., using to DL predict the evolution of a physical system.
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* Model reduction and time series predictions, i.e., using to DL predict the evolution of a physical system in a latent space.
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This typically replaces a numerical solver, and we can make use of special techniques from the DL area that target time series.
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* Generative models are likewise an own topic in DL, and here especially generative adversarial networks were shown to be powerful tools. They also represent a highly interesting training approach involving to separate NNs.
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{cite}`xie2018tempoGan`
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* Meshless methods and unstructured meshes are an important topic for classical simulations. Here, we'll look at a specific Lagrangian method that employs learning in the context of dynamic, particle-based representations.
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{cite}`prantl2019tranquil`
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@ -11,7 +11,9 @@ models, and there are lots of great introductions to deep learning.
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Hence, we'll keep it short:
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our goal is to approximate an unknown function
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$f^*(x) = y^*$ ,
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$$
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f^*(x) = y^* ,
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$$ (learn-base)
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where $y^*$ denotes reference or "ground truth" solutions.
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$f^*(x)$ should be approximated with an NN representation $f(x;\theta)$. We typically determine $f$
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@ -20,7 +22,9 @@ of the NN.
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This gives a minimization problem to find $f(x;\theta)$ such that $e$ is minimized.
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In the simplest case, we can use an $L^2$ error, giving
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$\text{arg min}_{\theta} | f(x;\theta) - y^* |_2^2$
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$$
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\text{arg min}_{\theta} | f(x;\theta) - y^* |_2^2
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$$ (learn-l2)
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We typically optimize, i.e. _train_,
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with some variant of a stochastic gradient descent (SGD) optimizer.
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@ -14,6 +14,24 @@
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@article{chu2021physgan,
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author = {Chu, Mengyu and Thuerey, Nils},
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title ={{Learning Meaningful Controls for Fluids}},
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journal = ACM_TOG,
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volume = {40(4)},
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year = {2021},
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publisher = {ACM},
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}
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% url={https://ge.in.tum.de/publications/tempogan/},
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@article{franz2021globtrans,
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author = {Franz, Erik and Solenthaler, Barbara and Thuerey, Nils},
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title ={{Global Transport for Fluid Reconstruction with Learned Self-Supervision}},
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journal = CVPR,
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year = {2021},
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url={https://ge.in.tum.de/publications/},
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}
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@article{um2020sol,
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title={Solver-in-the-Loop: Learning from Differentiable Physics to Interact with Iterative PDE-Solvers},
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author={Um, Kiwon and Brand, Robert and Holl, Philipp and Fei, Raymond Thuerey, Nils},
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@ -50,7 +68,6 @@
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url={https://ge.in.tum.de/publications/2019-tecogan-chu/},
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}
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@inproceedings{weiss2020ssc,
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title={Correspondence-Free Material Reconstruction using Sparse Surface Constraints},
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author={Weiss, Sebastian and Maier, Robert and Cremers, Daniel and Westermann, Rudiger and Thuerey, Nils},
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@ -696,25 +713,6 @@
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}
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@ARTICLE{ Thuerey:2007b:phd,
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AUTHOR = {N. Thuerey},
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TITLE = {{Physically based Animation of Free Surface Flows with the Lattice Boltzmann Method}},
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YEAR = {2007},
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JOURNAL = {PhD thesis},
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PUBLISHER = {Dept. of Computer Science 10, University of Erlangen-Nuremberg},
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VOLUME = {ISBN 978-3-89963-519-5}
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}
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@ARTICLE{ Thuerey:2006:drdobbs,
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AUTHOR = {N. Thuerey},
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TITLE = {{Fluid Simulation with Blender}},
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YEAR = {2006},
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JOURNAL = {Dr. Dobbs Journal},
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PUBLISHER = {CMP Media}
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}
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@ARTICLE{ Iglberger:2005:movNanoPart,
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AUTHOR = {Iglberger and N. Thuerey and U. Ruede and H. Schmid and W. Peukert},
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TITLE = {{Simulation of moving Nano-Particles with the Lattice Boltzmann Method in 3D}},
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@ -751,16 +749,6 @@
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}
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@ARTICLE{ Thuerey:2003:lbmMetallschaum,
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AUTHOR = {N. Thuerey and U. Ruede and C. Koerner},
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TITLE = {{Simulation von Metallschaum mittels der Lattice-Boltzmann Methode}},
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YEAR = {2003},
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JOURNAL = {Konwihr Quartl},
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PUBLISHER = {KONWIHR},
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VOLUME = {35}
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}
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@ARTICLE{ Thuerey:2003:singlePhaseFsLbm,
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AUTHOR = {N. Thuerey},
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TITLE = {{A Lattice Boltzmann method for single-phase free surface flows in 3D}},
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@ -781,7 +769,6 @@
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% ----------------- external --------------------
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