3.4. Local histogram matching

Local histogram matching in contrary to global history matching, where
histogram of the whole map is matched, calculates match of an density
map with an atom locally for each point of the whole unit cell map.

The following procedure ">utils/hist_match.com" generates electron
density of a single atom (sulphur) placed at the coordinate system
origin in a P1 cell with its' b-value equal to HIST_TEMP and
calculates convolution of the single atom with the underlaying map
using the convoluion theorem. (Structure factors of single atom map
are multiplied with structure factors of the underlaying map and then
backtransformed into a map.)

This procedure is intended to be called from other procedures as a
subprocedue, which, after a structure factor calculation and its storage
in the "fwork" array, multiplies it with the structure factors of the
histogram.  Product can be afterwards (after the return) transformed
into a map that serves for inspection or further calculations.

This file is made to be called from a solvent flattening procedure and
utilizes the MAP_SOLV for its structure factor calculation.  In your
own cases change the variable name or assign accordingly the MAP_SOLV
and HIST_TEMP values.

 main/utils/hist_match.com

> read atom
> *
> SGX

> set weight sele numb atom natom end 1.0
> set temp sele numb atom natom end HIST_TEMP
> make map MAP_SOLV zero
> make map MAP_SOLV conv real
> make map MAP_SOLV atom dens sele numb atom natom end 
> delete atom sele numb atom natom end 
> four map MAP_SOLV 
> reflect set ampl phase fwork = fwork * 1.0  *  fcalc * 1.0
> return