ac.phi: Murray...
In mpoll/scale: The Scaleable Langevin Exact Algorithm -- Reference Implementation

1	ac.phi(eta.pos, dapts)

`eta.pos`
`dapts`

##---- Should be DIRECTLY executable !! ----
##-- ==>  Define data, use random,
##--	or do  help(data=index)  for the standard data sets.

## The function is currently defined as
function (eta.pos, dapts) 
{
    beta.pos <- un.transform(eta.pos)
    data.evaluation <- data.eval(beta.pos, 1:dsz)
    (data.evaluation$grad.log.pi %*% t(data.evaluation$grad.log.pi) + 
        sum(data.evaluation$lap.log.pi))/2
  }