Partial differential equations
457 ideas in this subject. The map below lists the main ideas of the subject by area, in teaching order. 224 of its 225 ideas have a page so far.
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- ConceptPartial differential equation
A partial differential equation, or PDE, is an equation that relates an unknown function of several variables to its partial derivatives. It is the several-variable counterpart of an ordinary differential equation. PDEs describe heat flow, waves, fluids, electromagnetism, quantum mechanics and many other laws of physics, and they are central objects of geometry and probability. See the definition.
- ConceptOrder of a PDE
The order of a partial differential equation is the highest order of a partial derivative of the unknown function that occurs in it. It is the first number used to sort PDEs, and it controls how many initial or boundary conditions a well-posed problem needs. See the definition.
- ConceptLinear PDE
A linear PDE is a partial differential equation in which the unknown and its derivatives appear only linearly. Its coefficients depend on the variables alone. For a linear homogeneous equation, sums and multiples of solutions are again solutions. This superposition principle makes linear PDEs the best understood class, and it is the setting of Fourier methods, fundamental solutions and distribution theory. See the definition.
- ConceptSemilinear PDE
A semilinear PDE is a partial differential equation whose highest-order part is linear with coefficients depending only on the variables. Its lower-order terms may be nonlinear. The principal part, which decides the type of the equation, is then the same as for a linear equation. Many models of physics and biology have this form, such as reaction–diffusion equations and nonlinear wave equations. See the definition.
- ConceptQuasilinear PDE
A quasilinear PDE is a partial differential equation that is linear in the highest-order derivatives of the unknown. Its coefficients may depend on the unknown and its lower-order derivatives. This class contains the equations of fluid dynamics, the minimal surface equation and the p-Laplace equation. It sits between semilinear and fully nonlinear equations. See the definition.
- ConceptFully nonlinear PDE
A fully nonlinear PDE is a partial differential equation that depends nonlinearly on the highest-order derivatives of the unknown. Examples are the Monge–Ampère equation, the eikonal equation and the Hamilton–Jacobi equation. Such equations often lack classical solutions, and notions such as viscosity solutions were developed for them. See the definition.
Map of the subject
Basic notions and classification 23 of 23
- Partial differential equation definition
- Order of a PDE definition
- Linear PDE definition
- Semilinear PDE definition
- Quasilinear PDE definition
- Fully nonlinear PDE definition
- Principal symbol definition
- Characteristic variety definition
- Classification of second-order PDEs concept
- Elliptic partial differential equation definition
- Parabolic partial differential equation definition
- Hyperbolic partial differential equation definition
- Mixed-type equation definition
- Well-posed problem definition
- Initial value problem definition
- Boundary value problem definition
- Dirichlet problem problem
- Neumann problem problem
- Robin boundary condition definition
- Free boundary problem problem
- Stefan problem problem
- Obstacle problem problem
- Overdetermined system concept
Existence theory 8 of 8
- Cauchy–Kovalevskaya theorem statement
- Holmgren's uniqueness theorem statement
- Lewy's example counterexample
- Malgrange–Ehrenpreis theorem statement
- Fundamental solution definition
- Green's function definition
- Hadamard's example of ill-posedness counterexample
- Local solvability concept
Generalized solutions and function spaces 25 of 25
- Probability distribution definition
- Dirac delta function object
- Bump function definition
- Schwartz space definition
- Tempered distribution definition
- Weak derivative definition
- Weak solution definition
- Sobolev space definition
- Sobolev inequality statement
- Gagliardo–Nirenberg interpolation inequality statement
- Morrey's inequality statement
- Rellich–Kondrachov theorem statement
- Poincaré inequality statement
- Trace operator definition
- Hölder space definition
- Besov space definition
- Triebel–Lizorkin space definition
- Fractional Sobolev space definition
- Bessel potential definition
- Hardy inequality in Sobolev spaces statement
- Lax–Milgram theorem statement
- Galerkin method concept
- Viscosity solution definition
- Entropy solution definition
- Mild solution definition
Elliptic equations 37 of 37
- Laplace's equation definition
- Laplacian definition
- Harmonic function definition
- Mean value property statement
- Poisson's equation definition
- Poisson kernel definition
- Newtonian potential definition
- Maximum principle statement
- Hopf lemma statement
- Harnack's inequality statement
- Liouville's theorem for harmonic functions statement
- Weyl's lemma statement
- Dirichlet's principle statement
- Perron method concept
- Kelvin transform definition
- Schauder estimates statement
- Elliptic regularity statement
- Calderón–Zygmund estimates statement
- De Giorgi–Nash–Moser theorem statement
- Krylov–Safonov estimate statement
- Fredholm alternative statement
- Helmholtz equation definition
- Biharmonic equation definition
- p-Laplacian definition
- Monge–Ampère equation definition
- Minimal surface equation definition
- Bernstein's problem problem
- Plateau's problem problem
- Yamabe problem problem
- Liouville's equation definition
- Lane–Emden equation definition
- Mountain pass theorem statement
- Lopatinskii–Shapiro condition definition
- Elliptic boundary value problem definition
- Hypoelliptic operator definition
- Hörmander's condition definition
- Cauchy–Riemann operator definition
Parabolic equations 19 of 19
- Heat equation definition
- Heat kernel definition
- Parabolic maximum principle statement
- Tychonoff's non-uniqueness example counterexample
- Widder's theorem statement
- Reaction–diffusion system definition
- Fisher's equation definition
- Allen–Cahn equation definition
- Cahn–Hilliard equation definition
- Porous medium equation definition
- Fokker–Planck equation definition
- Black–Scholes equation definition
- Feynman–Kac formula statement
- Ricci flow definition
- Mean curvature flow definition
- Kardar–Parisi–Zhang equation definition
- Keller–Segel model definition
- Turing pattern concept
- Harnack inequality for parabolic equations statement
Hyperbolic equations 15 of 15
- Wave equation definition
- d'Alembert's formula statement
- Huygens principle statement
- Proof by infinite descent concept
- Finite speed of propagation statement
- Energy method concept
- Klein–Gordon equation definition
- Telegrapher's equations definition
- Strict hyperbolicity definition
- Strichartz estimate statement
- Dispersive partial differential equation definition
- Geometric optics concept
- Propagation of singularities statement
- Wave front set definition
- Christodoulou–Klainerman stability of Minkowski space statement
First-order equations and conservation laws 18 of 18
- Method of characteristics concept
- Transport equation definition
- Hamilton–Jacobi equation definition
- Eikonal equation definition
- Hopf–Lax formula statement
- Complete integral definition
- Conservation law definition
- Hyperbolic conservation law definition
- Burgers' equation definition
- Shock wave concept
- Rankine–Hugoniot conditions statement
- Riemann problem problem
- Rarefaction wave concept
- Glimm scheme concept
- Cole–Hopf transformation concept
- Lax–Friedrichs method concept
- Godunov's scheme concept
- Courant–Friedrichs–Lewy condition statement
Solution representations and transform methods 14 of 14
- Separation of variables concept
- Fourier series method concept
- Fourier transform definition
- Laplace transform definition
- Duhamel's principle statement
- Method of images concept
- Spherical harmonics object
- Similarity solution concept
- Traveling wave concept
- Lie group method for PDEs concept
- Bäcklund transform concept
- Inverse scattering transform concept
- Lax pair definition
- Soliton concept
Spectral theory and eigenvalue problems 11 of 11
- Dirichlet eigenvalue definition
- Rayleigh quotient definition
- Min-max theorem statement
- Weyl's law statement
- Faber–Krahn inequality statement
- Hearing the shape of a drum problem
- Schiffer's conjecture conjecture
- Pompeiu problem problem
- Schrödinger operator definition
- Steklov eigenvalue problem problem
- Cheeger constant definition
Qualitative behavior and nonlinear analysis 14 of 14
- A priori estimate concept
- Regularity theory concept
- Comparison principle statement
- Symmetric decreasing rearrangement concept
- Global attractor concept
- Homogenization concept
- Calculus of variations concept
- Euler–Lagrange equation definition
- Direct method in the calculus of variations concept
- Hilbert's nineteenth problem problem
- Hilbert's twentieth problem problem
- Leray–Schauder degree definition
- Nash–Moser theorem statement
- Aubin–Lions lemma statement
Equations of mathematical physics 24 of 24
- Schrödinger equation definition
- Nonlinear Schrödinger equation definition
- Korteweg–De Vries equation definition
- Sine-Gordon equation definition
- Kadomtsev–Petviashvili equation definition
- Navier–Stokes equations definition
- Navier–Stokes existence and smoothness conjecture
- Existence of Leray weak solutions statement
- Euler equations definition
- Stokes flow definition
- Boltzmann equation definition
- Vlasov equation definition
- Maxwell's equations definition
- Dirac equation definition
- Yang–Mills equations definition
- Einstein field equations definition
- Ginzburg–Landau equation definition
- Gross–Pitaevskii equation definition
- Hamilton–Jacobi–Bellman equation definition
- Mean-field game concept
- Lamé equations of elasticity definition
- Shallow water equations definition
- Darcy's law statement
- Tricomi equation definition
Pseudodifferential and microlocal methods 9 of 10
- Pseudo-differential operator definition
- Symbol class definition
- Fourier integral operator definition
- Microlocal analysis concept
- Atiyah–Singer index theorem statement
- Calderón projector definition
- Dirichlet-to-Neumann operator definition
- Calderón problem problem
- Fractional Laplacian definition
- Riesz potential definition
Further topics 7 of 7
- Stochastic partial differential equation definition
- Regularity structures concept
- Inverse problem concept
- Finite element method concept
- Finite difference method concept
- Lax equivalence theorem statement
- Optimal transport and the Monge problem problem
More ideas in this subject
Concepts 48
- Nonlinear potential theory
- Coercive bilinear form
- Dirichlet boundary condition
- Dirichlet energy
- Discrete Poisson equation
- FBI transform
- Integro-partial differential equation
- Jordan–Kinderlehrer–Otto scheme
- Spherical mean transform
- Heat potential
- MacCormack method
- Paraproduct
- Regularity of minimizers
- Tangential Cauchy–Riemann equations
- Weierstrass transform
- Barrier
- Discontinuous Galerkin method
- Elliptic operator
- Flux limiter
- Harmonic map heat flow
- Heat kernel on a Riemannian manifold
- Inertial manifold
- Lax–Wendroff method
- MUSCL scheme
- Riemann solver
- Total variation diminishing scheme
- Contact structure on a jet bundle
- Parametrix
- Complex powers of elliptic operators
- Differential operator between vector bundles
- Principal symbol of an operator on a manifold
- Spencer cohomology
- Elliptic operator on a compact manifold
- Finite volume method
- Natural boundary condition
- Neumann boundary condition
- Kolmogorov backward equation
- Polyharmonic function
- Caloric function
- Green's function for the Laplacian
- Level-set method
- Bateman transform
- p-harmonic function
- Fundamental solution of the Laplacian
- Lipschitz domain
- Displacement convexity
- Spectral geometry
- Spectrum of the Laplace–Beltrami operator
Theorems and results 32
- Gårding's inequality
- Benamou–Brenier formula
- Lieb–Thirring inequality
- Symmetry of the Green function
- Cheeger's inequality for the first eigenvalue
- Crandall–Lions uniqueness theorem
- Exterior cone condition
- Fast marching method
- Legendre–Hadamard condition
- Calderón–Vaillancourt theorem
- Cauchy–Kovalevskaya theorem for ODEs
- Dispersive estimate for the Schrödinger equation
- Minakshisundaram–Pleijel asymptotic expansion
- Viscosity solution of the Hamilton–Jacobi–Bellman equation
- Eells–Sampson theorem
- Godunov's theorem
- Hörmander's L2 estimates
- Lions–Stampacchia theorem
- Inversion of the Weierstrass transform
- Bombieri–De Giorgi–Giusti theorem
- Roe solver
- Strichartz estimates in Lorentz space
- Boundary Harnack principle
- Brenier's theorem
- Laplacian as a sum of second partial derivatives
- Dahlberg's theorem on harmonic measure
- Cartan–Kähler theorem
- Maximum principle for harmonic functions
- Minimum principle for harmonic functions
- Green's identities
- Removable singularities for harmonic functions
- Smoothness and analyticity of harmonic functions
Examples 8
Counterexamples 1
Problems 5
Conjectures 1
Definitions 174
- A priori estimate
- Coercive bilinear form
- Dirichlet boundary condition
- Dirichlet energy
- Discrete Poisson equation
- Entropy solution
- FBI transform
- Fourier transform
- Heat kernel
- Hyperbolic conservation law
- Hypoelliptic operator
- Integro-partial differential equation
- Inverse problem
- Jordan–Kinderlehrer–Otto scheme
- Lax–Friedrichs method
- Leray–Schauder degree
- Lie group method for PDEs
- Lopatinskii–Shapiro condition
- Parabolic partial differential equation
- Rarefaction wave
- Shock wave
- Similarity solution
- Spherical mean transform
- Traveling wave
- Wave front set
- Weak solution
- Well-posed problem
- Characteristic variety
- Elliptic boundary value problem
- Elliptic partial differential equation
- Fully nonlinear PDE
- Heat potential
- Homogenization
- Hyperbolic partial differential equation
- Inverse scattering transform
- Lax pair
- Local solvability
- MacCormack method
- Mean curvature flow
- Microlocal analysis
- Mixed-type equation
- Paraproduct
- Pseudo-differential operator
- Regularity of minimizers
- Regularity structures
- Regularity theory
- Ricci flow
- Soliton
- Strict hyperbolicity
- Tangential Cauchy–Riemann equations
- Telegrapher's equations
- Weierstrass transform
- Barrier
- Classification of second-order PDEs
- Direct method in the calculus of variations
- Discontinuous Galerkin method
- Einstein field equations
- Elliptic operator
- Flux limiter
- Fourier series method
- Glimm scheme
- Godunov's scheme
- Harmonic map heat flow
- Heat kernel on a Riemannian manifold
- Inertial manifold
- Lax–Wendroff method
- Method of images
- MUSCL scheme
- Riemann solver
- Robin boundary condition
- Total variation diminishing scheme
- Burgers' equation
- Bäcklund transform
- Complete integral
- Conservation law
- Contact structure on a jet bundle
- Fourier integral operator
- Fractional Sobolev space
- Korteweg–De Vries equation
- Parametrix
- Sine-Gordon equation
- Symbol class
- Viscosity solution
- Weak derivative
- Black–Scholes equation
- Calculus of variations
- Cole–Hopf transformation
- Complex powers of elliptic operators
- Differential operator between vector bundles
- Dirac equation
- Fisher's equation
- Fundamental solution
- Hölder space
- Hörmander's condition
- Kadomtsev–Petviashvili equation
- Kardar–Parisi–Zhang equation
- Shallow water equations
- Symmetric decreasing rearrangement
- Fokker–Planck equation
- Method of characteristics
- Principal symbol of an operator on a manifold
- Spencer cohomology
- Boltzmann equation
- Dispersive partial differential equation
- Eikonal equation
- Elliptic operator on a compact manifold
- Finite volume method
- Hamilton–Jacobi equation
- Monge–Ampère equation
- Natural boundary condition
- Neumann boundary condition
- Transport equation
- Tricomi equation
- Linear PDE
- Maxwell's equations
- Order of a PDE
- Principal symbol
- Quasilinear PDE
- Semilinear PDE
- Separation of variables
- Vlasov equation
- Geometric optics
- Partial differential equation
- Euler equations
- Ginzburg–Landau equation
- Allen–Cahn equation
- Gross–Pitaevskii equation
- Heat equation
- Helmholtz equation
- Keller–Segel model
- Kolmogorov backward equation
- Lamé equations of elasticity
- Lane–Emden equation
- Laplace's equation
- Minimal surface equation
- Navier–Stokes equations
- Polyharmonic function
- Schrödinger operator
- Stokes flow
- Wave equation
- Biharmonic equation
- Cahn–Hilliard equation
- Caloric function
- Energy method
- Fractional Laplacian
- Klein–Gordon equation
- Liouville's equation
- Mean-field game
- Nonlinear Schrödinger equation
- p-Laplacian
- Porous medium equation
- Reaction–diffusion system
- Schrödinger equation
- Dirichlet eigenvalue
- Green's function for the Laplacian
- Level-set method
- Turing pattern
- Bateman transform
- p-harmonic function
- Poisson's equation
- Calderón projector
- Cauchy–Riemann operator
- Fundamental solution of the Laplacian
- Euler–Lagrange equation
- Laplacian
- Lipschitz domain
- Displacement convexity
- Perron method
- Spectral geometry
- Dirichlet-to-Neumann operator
- Global attractor
- Spectrum of the Laplace–Beltrami operator
- Stochastic partial differential equation
- Galerkin method