Description:
<jats:p>The time-independent wave equation, d2ψ/dz2+Q2(z)ψ=0, where Q2(z) may have arbitrary order zeros and poles on or close to the real axis, is transformed to a simpler wave equation of similar properties (model). Approximate transformations leading from the original wave equation to the model are simply related to Fröman’s higher-order phase integrals, but are nevertheless well defined at the pertinent zeros and poles of Q2(z).</jats:p>