
It is shown that the disconjugate equation (1) L x ≡ ( 1 / β n ) ( d / d t ) ⋅ ( 1 / β n − 1 ) ⋯ ( d / d t ) ( 1 / β 1 ) ( d / d t ) ( x / β 0 ) = 0 Lx \equiv (1/{\beta _n})(d/dt) \cdot (1/{\beta _{n - 1}}) \cdots (d/dt)(1/{\beta _1})(d/dt)(x/{\beta _0}) = 0 , a > t > b > t > b , where β i > 0 {\beta _i} > 0 , and (2) β i ∈ C ( a , b ) {\beta _i} \in C(a,b) , can be written in essentially unique canonical forms so that ∫ b β i d t = ∞ ( ∫ a β i d t = ∞ ) {\smallint ^b}{\beta _i}dt = \infty ({\smallint _a}{\beta _i}dt = \infty ) for 1 ≤ i ≤ n − 1 1 \leq i \leq n - 1 . From this it follows easily that (1) has solutions x 1 , … , x n {x_1}, \ldots ,{x_n} which are positive in (a, b) near b ( a ) b(a) and satisfy lim t → b − x i ( t ) / x j ( t ) = 0 ( lim t → a + x i ( t ) / x j ( t ) = ∞ ) {\lim _{t \to b}} - {x_i}(t)/{x_j}(t) = 0({\lim _{t \to a}} + {x_i}(t)/{x_j}(t) = \infty ) for 1 ≤ i > j ≤ n 1 \leq i > j \leq n . Necessary and sufficient conditions are given for (1) to have solutions y 1 , … , y n {y_1}, \ldots ,{y_n} such that lim t → b − y i ( t ) / y j ( t ) = lim t → a + y j ( t ) / y i ( t ) = 0 {\lim _{t \to b}} - {y_i}(t)/{y_j}(t) = {\lim _{t \to a}} + {y_j}(t)/{y_i}(t) = 0 for 1 ≤ i > j ≤ n 1 \leq i > j \leq n . Using different methods, P. Hartman, A. Yu. Levin and D. Willett have investigated the existence of fundamental systems for (1) with these properties under assumptions which imply the stronger condition ( 2 ′ ) β i ∈ C ( n − i ) ( a , b ) (2’){\beta _i} \in {C^{(n - i)}}(a,b) .
Qualitative theory for ordinary differential equations, Oscillation theory, zeros, disconjugacy and comparison theory for ordinary differential equations
Qualitative theory for ordinary differential equations, Oscillation theory, zeros, disconjugacy and comparison theory for ordinary differential equations
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