Neural networks can be used as a method for efficiently solving difficult partial differential equations. Recently this strategy has been dubbed physics-informed neural networks and has seen a resurgence because of its efficiency advantages over classical deep learning. Efficient implementations from recent papers are being explored as part of the NeuralNetDiffEq.jl package. The issue tracker contains links to papers which would be interesting new neural network based methods to implement and benchmark against classical techniques. Project work in this area includes:

Improved training strategies for PINNs.

Implementing new neural architectures that impose physical constraints like divergence-free criteria.

Demonstrating large-scale problems solved by PINN training.

Improving the speed and parallelization of PINN training routines.

This project is good for both software engineers interested in the field of scientific machine learning and those students who are interested in perusing graduate research in the field.

**Recommended Skills**: Background knowledge in numerical analysis and machine learning.

**Expected Results**: New neural network based solver methods.

**Mentors**: Chris Rackauckas and Kirill Zubov

Neural ordinary differential equations have been shown to be a way to use machine learning to learn differential equation models. Further improvements to the methodology, like universal differential equations have incorporated physical and biological knowledge into the system in order to make it a data and compute efficient learning method. However, there are many computational aspects left to explore. The purpose of this project is to enhance the universal differential equation approximation abilities of DiffEqFlux.jl, adding features like:

Improved adjoints for DAEs and SDEs

Various improvements to minibatching

Support for second order ODEs (i.e. symplectic integrators)

See the DiffEqFlux.jl issue tracker for full details.

This project is good for both software engineers interested in the field of scientific machine learning and those students who are interested in perusing graduate research in the field.

**Recommended Skills**: Background knowledge in numerical analysis and machine learning.

**Expected Results**: New and improved methods for neural and universal differential equations.

**Mentors**: Chris Rackauckas

In many cases, when attempting to optimize a function `f(p)`

each calculation of `f`

is very expensive. For example, evaluating `f`

may require solving a PDE or other applications of complex linear algebra. Thus, instead of always directly evaluating `f`

, one can develop a surrogate model `g`

which is approximately `f`

by training on previous data collected from `f`

evaluations. This technique of using a trained surrogate in place of the real function is called surrogate optimization and mixes techniques from machine learning to accelerate optimization.

Advanced techniques utilize radial basis functions and Gaussian processes in order to interpolate to new parameters to estimate `f`

in areas which have not been sampled. Adaptive training techniques explore how to pick new areas to evaluate `f`

to better hone in on global optima. The purpose of this project is to explore these techniques and build a package which performs surrogate optimizations.

**Recommended Skills**: Background knowledge of standard machine learning, statistical, or optimization techniques. Strong knowledge of numerical analysis is helpful but not required.

**Expected Results**: Library functions for performing surrogate optimization with tests on differential equation models.

**Mentors**: Chris Rackauckas

Machine learning has become a popular tool for understanding data, but scientists typically understand the world through the lens of physical laws and their resulting dynamical models. These models are generally differential equations given by physical first principles, where the constants in the equations such as chemical reaction rates and planetary masses determine the overall dynamics. The inverse problem to simulation, known as parameter estimation, is the process of utilizing data to determine these model parameters.

The purpose of this project is to utilize the growing array of statistical, optimization, and machine learning tools in the Julia ecosystem to build library functions that make it easy for scientists to perform this parameter estimation with the most high-powered and robust methodologies. Possible projects include improving methods for Bayesian estimation of parameters via Stan.jl and Julia-based libraries like Turing.jl, or global optimization-based approaches. Novel techniques like classifying model outcomes via support vector machines and deep neural networks can also be considered. Research and benchmarking to attempt to find the most robust methods will take place in this project. Additionally, the implementation of methods for estimating structure, such as topological sensitivity analysis along with performance enhancements to existing methods will be considered.

Some work in this area can be found in DiffEqParamEstim.jl and DiffEqBayes.jl. Examples can be found in the DifferentialEquations.jl documentation.

**Recommended Skills**: Background knowledge of standard machine learning, statistical, or optimization techniques. It's recommended but not required that one has basic knowledge of differential equations and DifferentialEquations.jl. Using the differential equation solver to get outputs from parameters can be learned on the job, but you should already be familiar (but not necessarily an expert) with the estimation techniques you are looking to employ.

**Expected Results**: Library functions for performing parameter estimation and inferring properties of differential equation solutions from parameters. Notebooks containing benchmarks determining the effectiveness of various methods and classifying when specific approaches are appropriate will be developed simultaneously.

**Mentors**: Chris Rackauckas, Vaibhav Dixit

Scientific machine learning requires mixing scientific computing libraries with machine learning. This blog post highlights how the tooling of Julia is fairly advanced in this field compared to alternatives such as Python, but one area that has not been completely worked out is integration of automatic differentiation with partial differential equations. FEniCS.jl is a wrapper to the FEniCS project for finite element solutions of partial differential equations. We would like to augment the Julia wrappers to allow for integration with Julia's automatic differentiation libraries like Zygote.jl by using dolfin-adjoint. This would require setting up this library for automatic installation for Julia users and writing adjoint passes which utilize this adjoint builder library. It would result in the first total integration between PDEs and neural networks.

**Recommended Skills**: A basic background in differential equations and Python. Having previous Julia knowledge is preferred but not strictly required.

**Expected Results**: Efficient and high-quality implementations of adjoints for Zygote.jl over FEniCS.jl functions.

**Mentors**: Chris Rackauckas

While standard machine learning can be shown to be "safe" for local optimization, scientific machine learning can sometimes require the use of globalizing techniques to improve the optimization process. Hybrid methods, known as multistart optimization methods, glue together a local optimization technique together with a parameter search over a large space of possible initial points. The purpose of this project would be to take a MultistartOptimization.jl as a starting point and create a fully featured set of multistart optimization tools for use with Optim.jl

**Recommended Skills**: A basic background in optimization. Having previous Julia knowledge is preferred but not strictly required.

**Expected Results**: Efficient and high-quality implementations of multistart optimization methods.

**Mentors**: Chris Rackauckas and Patrick Kofod Mogensen

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