We consider the differential
operator l(y) = y′′ + qy, where q is a positive, continuously differentiable function
defined on a ray [a,∞). The operator l determines, with appropriate restrictions,
self-adjoint operators defined in the hilbert space ℒ2[a,∞) of quadratically
summable, complexvalued functions on [a,∞). In this note, we prove that if L is such
a selfadjoint operator, then the conditions q(t) →∞ and q′(t)q(t)−1∕2 → 0 as t →∞
are sufficient for the continuous spectrum C(L) of L to cover the entire real
axis.
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