A Quantitative Comparison Theorem for Nonlinear Equations

In the present paper we establish a quantitative comparison theorem for positive solutions of the following initial value problems 8 < : (p 1 (r)(u)ju 0 j m?2 u 0) 0 + q 1 (r)f(u) = 0 u(0) = u 0 ; u 0 (0) = 0 and 8 < : (p 2 (r)(v)jv 0 j m?2 v 0) 0 + q 2 (r)f(v) = 0 v(0) = v 0 ; v 0 (0) = 0 with r > 0 and m > 1, and also show some applications of the theorem to the non-existence problem of positive solutions of quasilinear equations. Basic models leading to such nonlinear equations are the degenerate Laplace equation, and the steady state porous medium equation.