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WKB approximation
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<p>In <a href="/facts/Mathematical_physics/sLKg8T1G">mathematical physics</a>, the WKB approximation or WKB method is a technique for finding approximate solutions to <a href="/facts/Linear_differential_equation/nLEbIIVf">linear differential equations</a> with spatially varying coefficients. It is typically used for a <a href="/facts/Semiclassical_physics/8v1CG3RP">semiclassical</a> calculation in <a href="/facts/Quantum_mechanics/BRc3Mzgr">quantum mechanics</a> in which the <a href="/facts/Wave_function/KgM5ykjY">wave function</a> is recast as an exponential function, semiclassically expanded, and then either the amplitude or the phase is taken to be changing slowly. </p><p>The name is an initialism for Wentzel–Kramers–Brillouin. It is also known as the LG or Liouville–Green method. Other often-used letter combinations include JWKB and WKBJ, where the "J" stands for Jeffreys. </p>