Consider the Sturm-Liouville problem (pu') + Vu = 0 for the function u(x), with p(x) > 0 and V(x) = q(x) + lambda p(x).
(a) Perform the Prufer substitution u - r sin theta and u'p = r cos theta and obtain the Prufer equations for the amplitude r(x) and the phase theta (x):
r' - 1/2 ((1/p) - v) r sin 2 theta, theta' = (1/p)cos^2 theta + V sin^2 theta.
(b) Show that the phase theta is an increasing function at each zero of u(x).
(c) Show that, if V(x) > 0, u(x) has exactly one maximum/minimum between two consecutive zeros.© BrainMass Inc. brainmass.com March 4, 2021, 5:52 pm ad1c9bdddf
This shows how to perform a prufer substitution and find prufer equations, show that the phase is an increasing function, and show that there is exactly one maximum/minimum between consecutive zeroes.