Liouville–Bratu–Gelfand equation


In mathematics, Liouville–Bratu–Gelfand equation or Liouville's equation is a non-linear Poisson equation, named after the mathematicians Joseph Liouville, G. Bratu and Israel Gelfand. The equation reads
The equation appears in thermal runaway as Frank-Kamenetskii theory, astrophysics for example, Emden–Chandrasekhar equation. This equation also describes space charge of electricity around a glowing wire and describes planetary nebula.

Liouville's solutionBateman, Harry. "Partial differential equations of mathematical physics." Partial Differential Equations of Mathematical Physics, by H. Bateman, Cambridge, UK: Cambridge University Press, 1932 (1932).

In two dimension with Cartesian Coordinates, Joseph Liouville proposed a solution in 1853 as
where is an arbitrary analytic function with. In 1915, G.W. Walker found a solution by assuming a form for. If, then Walker's solution is
where is some finite radius. This solution decays at infinity for any, but becomes infinite at the origin for , becomes finite at the origin for and becomes zero at the origin for. Walker also proposed two more solutions in his 1915 paper.

Radially symmetric forms

If the system to be studied is radially symmetric, then the equation in dimension becomes
where is the distance from the origin. With the boundary conditions
and for, a real solution exists only for, where is the critical parameter called as Frank-Kamenetskii parameter. The critical parameter is for, for and for. For, two solution exists and for infinitely many solution exists with solutions oscillating about the point. For, the solution is unique and in these cases the critical parameter is given by. Multiplicity of solution for was discovered by Israel Gelfand in 1963 and in later 1973 generalized for all by Daniel D. Joseph and Thomas S. Lundgren.