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[ENH] explicit/analytic form of energy function for log-normal distribution #219

@fkiraly

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@fkiraly

There does not seem to exist a literature reference for the energy functionals of the log-normal distribution, we should try to derive it, or find a reference.

Collecting discussion below, from #214.

Current state:

  • explicit formula for the cross-term $\mathbb{E}[|X-c|]$ (almost) derived
  • no progress yet on the self-term $\mathbb{E}[|X-X'|]$

@bhavikar04 used Wolfram Alpha to derive the following indefinite integral related to the cross-term $\mathbb{E}[X-c]$:
Screenshot 2024-03-23 130300

My reply:
this looks correct. Now you need to add the limits. That should be an easy substitution, no? I recommend, do that manually. Use that

$\lim_{x\rightarrow -\infty} \mbox{erf}(x) = -1$, and $\lim_{x\rightarrow \infty} \mbox{erf}(x) = 1$. You need to be careful with the sign, but that should be it?

The number 0.707 etc should be $\frac{1}{2} \sqrt{2}$, but it doesn't matter for the limits.

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    implementing algorithmsImplementing algorithms, estimators, objects native to skpromath&theorymathematical derivations, theory developmentmodule:probability&simulationprobability distributions and simulators

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