Disconjugacy of complex differential systems
Binyamin Schwarz · Transactions of the American Mathematical Society · 1966
where the real (or complex) functions aik(x) are continuous on the interval a < x < b. From the coefficients aik(x) Nehari built a matrix A with nonnegative constants as elements. Denoting the maximal characteristic value of A by A(A), he showed that A(A) < 1 ensures the disconjugacy of (1) in the sense defined below [7, Theorem III]. His proof, based on a variational property of A(A), holds also for the complex system