Probability distribution of a stochastic variable

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The discussion focuses on the probability distribution of a stochastic variable defined by a generator functional in the context of a specific article. The generator functional G[h] is expressed in terms of an expectation value involving a stochastic potential V and an arbitrary function h. The author equates this functional to a specific exponential form, suggesting a relationship between the functions involved. Participants seek clarification on the mathematical steps to derive this relationship and express confusion regarding the author's justification. Further references or hints for understanding the derivation are requested.
Ravi Mohan
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I am studying an article which involves stochastic variables http://www.rmki.kfki.hu/~diosi/prints/1985pla112p288.pdf.

The author defines a probability distribution of a stochastic potential V by a generator functional
<br /> G[h] = \left&lt;exp\left(i\int V(\vec{r},t)h(\vec{r},t)d\vec{r}dt\right)\right&gt;,<br />
where h is an arbitrary function and \langle\rangle stands for expectation values evaluated by means of the probabil-
ity distribution of V.

He, then equates it to (equation 1 in the article)
<br /> G[h] = exp\left(-\frac{1}{2}\iint h(\vec{r},t)h(\vec{r}^{\prime},t)f(\vec{r}-\vec{r}^{\prime})d\vec{r}d\vec{r}^{\prime}dt\right).<br />

How do we mathematically work out the steps? Any relevant reference or hint will be of great help. Thanks.
 
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I don't understand the author's justification. However it looks like something of the form:

&lt;\sqrt(A,A*)&gt;, where A is the exponential integral.
 
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