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How/when can I take a wave function and its complex conjugate as independent?

  1. May 18, 2012 #1
    For the last step in the derivation of the Gross-Pitaevskii equation, we have the following equation
    [itex]0=\int \eta^*(gNh\phi+gN^2\phi^*\phi^2-N\mu\phi)\ dV+\int (N\phi^*h+gN^2(\phi^2)^*\phi-N\mu\phi^*)\eta\ dV,[/itex]
    where [itex]\eta[/itex] is an arbitrary function, [itex]g,N,\mu[/itex] are constants, [itex]h[/itex] is the hamiltonian for the harmonic oscillator and [itex]\phi[/itex] is the ground state of the hamiltonian.

    Now, the last step involves seeing that this can only be the case if [itex]gNh\phi+gN^2\phi^*\phi^2-N\mu\phi[/itex] and [itex]N\phi^*h+gN^2(\phi^2)^*\phi-N\mu\phi^*[/itex] are both zero. As far as I can tell, I would need an argument that [itex]\phi[/itex] and [itex]\phi^*[/itex] are independent for this to be true.

    Can anyone explain why this is the case (or in case I'm wrong, explain what else I need to consider)?

  2. jcsd
  3. May 18, 2012 #2


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    Write it as ∫ η* A dV + ∫ η B dV = 0, and let η = α + i β where α, β are arbitrary real functions. Then ∫ [α (A + B) + β (-iA + iB)] dV = 0. This can only happen if A + B and A - B are both zero, in other words A and B are both zero. You don't have to assume anything about φ.
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