This Letter presents an algorithm to obtain all local conservation laws for any system of field e... more This Letter presents an algorithm to obtain all local conservation laws for any system of field equations. The algorithm uses a formula which directly generates the conservation laws and does not depend on the system having a Lagrangian formulation, in contrast to Noether's theorem which requires a Lagrangian. Several examples are considered including dissipative systems inherently having no Lagrangian.
ABSTRACT The wave equation c2(x)uxx−utt=0 is solved for wave speeds c(x) corresponding to two-lay... more ABSTRACT The wave equation c2(x)uxx−utt=0 is solved for wave speeds c(x) corresponding to two-layered media with smooth transition from layer to layer. The wave speed c(x) has four free parameters to fit a given medium. Solutions are constructed from invariant solutions of a related system of first-order partial differential equations that admit a four-parameter symmetry group. These solutions are superposed to solve general initial value problems for data with compact support; the computation of the superposition coefficients uses elementary Fourier analysis. Solutions are illustrated for various initial conditions.
Journal of Mathematical Analysis and Applications, 1989
Group analysis is applied to overdetermined systems of ODES. If each ODE of the system admits the... more Group analysis is applied to overdetermined systems of ODES. If each ODE of the system admits the same r-parameter solvable Lie group, then the use of the corresponding differential invariants greatly simplifies the analysis of the system. Moreover this can even lead to its explicit solution. Examples are given.
Journal of Mathematical Analysis and Applications, 2006
Two formulas are introduced to directly obtain new conservation laws for any system of partial di... more Two formulas are introduced to directly obtain new conservation laws for any system of partial differential equations from a known conservation law and admitted symmetries. The first formula maps any conservation law of a given system to the corresponding conservation law of the system obtained through a contact transformation. When the contact transformation is a symmetry of the given system, then the corresponding conservation law is a conservation law of the given system. The second formula checks a priori whether or not the action of a symmetry (continuous or discrete) on a conservation law can yield one or more new conservation laws of the given system. Several examples are considered, including the use of a discrete symmetry to obtain a new conservation law and the use of a continuous symmetry to generate two new conservation laws.
This paper gives a general treatment and proof of the direct conservation law method presented in... more This paper gives a general treatment and proof of the direct conservation law method presented in Part I (see Anco & Bluman [3]). In particular, the treatment here applies to finding the local conservation laws of any system of one or more partial differential equations expressed in a standard Cauchy-Kovalevskaya form. A summary of the general method and its effective computational implementation is also given.
Simple and systematic algorithms for relating differential equations are given. They are based on... more Simple and systematic algorithms for relating differential equations are given. They are based on comparing the local symmetries admitted by the equations. Comparisons of the infinitesimal generators and their Lie algebras of given and target equations lead to necessary conditions for the existence of mappings which relate them. Necessary and sufficient conditions are presented for the existence of invertible mappings from a given nonlinear system of partial differential equations to some linear system of equations with examples including the hodograph and Legendre transformations, and the linearizations of a nonlinear telegraph equation, a nonlinear diffusion equation, and nonlinear fluid flow equations. Necessary and sufficient conditions are also given for the existence of an invertible point transformation which maps a linear partial differential equation with variable coefficients to a linear equation with constant coefficients. Other types of mappings are also considered inclu...
An algorithmic method using conservation law multipliers is introduced that yields necessary and ... more An algorithmic method using conservation law multipliers is introduced that yields necessary and sufficient conditions to find invertible mappings of a given nonlinear PDE to some linear PDE and to construct such a mapping when it exists. Previous methods yielded such conditions from admitted point or contact symmetries of the nonlinear PDE. Through examples, these two linearization approaches are contrasted.
This Letter presents an algorithm to obtain all local conservation laws for any system of field e... more This Letter presents an algorithm to obtain all local conservation laws for any system of field equations. The algorithm uses a formula which directly generates the conservation laws and does not depend on the system having a Lagrangian formulation, in contrast to Noether's theorem which requires a Lagrangian. Several examples are considered including dissipative systems inherently having no Lagrangian.
ABSTRACT The wave equation c2(x)uxx−utt=0 is solved for wave speeds c(x) corresponding to two-lay... more ABSTRACT The wave equation c2(x)uxx−utt=0 is solved for wave speeds c(x) corresponding to two-layered media with smooth transition from layer to layer. The wave speed c(x) has four free parameters to fit a given medium. Solutions are constructed from invariant solutions of a related system of first-order partial differential equations that admit a four-parameter symmetry group. These solutions are superposed to solve general initial value problems for data with compact support; the computation of the superposition coefficients uses elementary Fourier analysis. Solutions are illustrated for various initial conditions.
Journal of Mathematical Analysis and Applications, 1989
Group analysis is applied to overdetermined systems of ODES. If each ODE of the system admits the... more Group analysis is applied to overdetermined systems of ODES. If each ODE of the system admits the same r-parameter solvable Lie group, then the use of the corresponding differential invariants greatly simplifies the analysis of the system. Moreover this can even lead to its explicit solution. Examples are given.
Journal of Mathematical Analysis and Applications, 2006
Two formulas are introduced to directly obtain new conservation laws for any system of partial di... more Two formulas are introduced to directly obtain new conservation laws for any system of partial differential equations from a known conservation law and admitted symmetries. The first formula maps any conservation law of a given system to the corresponding conservation law of the system obtained through a contact transformation. When the contact transformation is a symmetry of the given system, then the corresponding conservation law is a conservation law of the given system. The second formula checks a priori whether or not the action of a symmetry (continuous or discrete) on a conservation law can yield one or more new conservation laws of the given system. Several examples are considered, including the use of a discrete symmetry to obtain a new conservation law and the use of a continuous symmetry to generate two new conservation laws.
This paper gives a general treatment and proof of the direct conservation law method presented in... more This paper gives a general treatment and proof of the direct conservation law method presented in Part I (see Anco & Bluman [3]). In particular, the treatment here applies to finding the local conservation laws of any system of one or more partial differential equations expressed in a standard Cauchy-Kovalevskaya form. A summary of the general method and its effective computational implementation is also given.
Simple and systematic algorithms for relating differential equations are given. They are based on... more Simple and systematic algorithms for relating differential equations are given. They are based on comparing the local symmetries admitted by the equations. Comparisons of the infinitesimal generators and their Lie algebras of given and target equations lead to necessary conditions for the existence of mappings which relate them. Necessary and sufficient conditions are presented for the existence of invertible mappings from a given nonlinear system of partial differential equations to some linear system of equations with examples including the hodograph and Legendre transformations, and the linearizations of a nonlinear telegraph equation, a nonlinear diffusion equation, and nonlinear fluid flow equations. Necessary and sufficient conditions are also given for the existence of an invertible point transformation which maps a linear partial differential equation with variable coefficients to a linear equation with constant coefficients. Other types of mappings are also considered inclu...
An algorithmic method using conservation law multipliers is introduced that yields necessary and ... more An algorithmic method using conservation law multipliers is introduced that yields necessary and sufficient conditions to find invertible mappings of a given nonlinear PDE to some linear PDE and to construct such a mapping when it exists. Previous methods yielded such conditions from admitted point or contact symmetries of the nonlinear PDE. Through examples, these two linearization approaches are contrasted.
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Papers by George Bluman