# Partial Differential Equation (PDE) Solvers Overview

## NeuralPDE.jl: Physics-Informed Neural Network (PINN) PDE Solvers

NeuralPDE.jl is a partial differential equation solver library which uses physics-informed neural networks (PINNs) to solve the equations. It uses the ModelingToolkit.jl symbolic PDESystem as its input and can handle a wide variety of equation types, including systems of partial differential equations, partial differential-algebraic equations, and integro-differential equations. Its benefit is its flexibility, and it can be used to easily generate surrogate solutions over entire parameter ranges. However, its downside is solver speed: PINN solvers tend to be a lot slower than other methods for solving PDEs.

## MethodOflines.jl: Automated Finite Difference Method (FDM)

MethodOflines.jl is a partial differential equation solver library which automates the discretization of PDEs via the finite difference method. It uses the ModelingToolkit.jl symbolic PDESystem as its input, and generates AbstractSystems and SciMLProblems whose numerical solution gives the solution to the PDE.

## FEniCS.jl: Wrappers for the Finite Element Method (FEM)

FEniCS.jl is a wrapper for the popular FEniCS finite element method library.

## HighDimPDE.jl: Scientific Machine Learning for Special High Dimensional PDE Forms

HighDimPDE.jl is a library of methods for high-dimensional non-local parabolic partial differential equations. It uses special problem types for specifying problems in these domains.

## NeuralOperators.jl: (Fourier) Neural Operators and DeepONets for PDE Solving

NeuralOperators.jl is a library for operator learning based PDE solvers. This includes techniques like:

• Fourier Neural Operators (FNO)
• Deep Operator Networks (DeepONets)
• Markov Neural Operators (MNO)

Currently its connection to PDE solving must be specified manually, though an interface for ModelingToolkit PDESystems is in progress.

## DiffEqOperators.jl: Operators for Finite Difference Method (FDM) Discretizations

DiffEqOperators.jl is a library for defining finite difference operators to easily perform manual FDM semi-discretizations of partial differential equations. This library is fairly incomplete and most cases should receive better performance using MethodOflines.jl.

# Third Party Libraries to Note

## ApproxFun.jl: Automated Spectral Discretizations

ApproxFun.jl is a package for approximating functions in basis sets. One particular use case is with spectral basis sets, such as Chebyshev functions and Fourier decompositions, making it easy to represent spectral and pseudospectral discretizations of partial differential equations as ordinary differential equations for the SciML equation solvers.

## Gridap.jl: Julia-Basd Tools for Finite Element Discretizations

Gridap.jl is a package for grid-based approximation of partial differential equations, particularly notable for its use of conforming and nonconforming finite element (FEM) discretizations.

## Trixi.jl: Adaptive High-Order Numerical Simulations of Hyperbolic Equations

Trixi.jl is a package for numerical simulation of hyperbolic conservation laws, i.e. a large set of hyperbolic partial differential equations, which interfaces and uses the SciML ordinary differential equation solvers.

## VoronoiFVM.jl: Tools for the Voronoi Finite Volume Discretizations

VoronoiFVM.jl is a library for generating FVM discretizations of systems of PDEs. It interfaces with many of the SciML equation solver libraries to allow for ease of discretization and flexibility in the solver choice.