Singular perturbations for parabolic equations with unbounded coefficients leading to ultraparabolic equations. (English) Zbl 1164.35312

Summary: Linear parabolic equations with coefficients of the lower-order terms unbounded and with a small parameter multiplying some of the second (highest) space derivatives are considered, in the limiting case when such a parameter goes to zero. This yields a degenerate parabolic (ultraparabolic) equation with one space-like variable, \(x\), and two time-like variables, \(y\) and \(t\). No boundary-layer is found to be needed in the case of the boundary-value problem on the \(x\)-unbounded domain \(Q_T=\{(x,y,t)\in \mathbb R\times [0,1]\times [0,T]\}\) with a periodic boundary condition in the variable \(y\) and initial data at \(t=0\).


35B25 Singular perturbations in context of PDEs
35F15 Boundary value problems for linear first-order PDEs
35F30 Boundary value problems for nonlinear first-order PDEs
35K20 Initial-boundary value problems for second-order parabolic equations