cmf_indicator_kernel: Indicator kernel
In conmolfields: Continuous molecular fields

Indicator kernel

1	cmf_indicator_kernel(mol1, mol2, alpha, syb_type)

`mol1`
`mol2`
`alpha`
`syb_type`

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

## The function is currently defined as
cmf_indicator_kernel <- function(mol1, mol2, alpha, syb_type) {
  res <- 0.0
  natoms1 <- length(mol1$atoms)
  natoms2 <- length(mol2$atoms)
  for (iatom1 in 1:natoms1) {
    atom1 <- mol1$atoms[[iatom1]]
    if(atom1$syb != syb_type) next
    for (iatom2 in 1:natoms2) {
      atom2 <- mol2$atoms[[iatom2]]
      if(atom2$syb != syb_type) next
      dist2 <- eucldist2(atom1, atom2)
      res <- res + exp(- alpha * dist2 / 4.0)
    }
  }
  coef <- sqrt(pi^3 / alpha^3)
  res <- coef * res
  res
}