Distances combine
distances_combine
Parameters
- selection=string
- (default: none)
- distance=dsum|dsumav|dmax
- (default: dsum)
- support=real range
- (default: 0.0..1.0E10)
- weightkeep=real
- (default: -1.0)
- combination=fourfour|twoone
- (default: fourfour)
- sort=level|individual|residue
- (default: level)
- equal
Description
This command applies "constraint combination" for the distance restraints that match the given selection. By default, the selection made in the most recent distances select command is used, or all distance restraints if no selection has been made so far.
Constraint combination is normally applied to reduce the impact of erroneous distance restraints that may be generated in the initial cycles of combined automated NOESY assignment and structure calculation using the noeassign command.
Only distance restraints with a support score in the range given by the support parameter are combined.
By default, or by setting combination=fourfour, four new ambiguous distance restraints are formed from four selected individual restraints A, B, C, D by combining the assignments from restraints A and B, A and C, A and D, and B and C, respectively. The assignments of restraint A are thus used in three of the new restraints, those from restraints B and C are used twice, and those from restraint D once. If the option equal is set, then the four new restraints are instead formed from by combining the assignments from restraints A and C, A and D, B and D, and B and C, respectively, i.e. the assignments from of the each input restraints are used are used twice to form a combined restraint. Alternatively, by setting combination=twoone, one new ambiguous distance restraint is formed from wach pair of selected individual restraints A and B by combining their assignments.
The input restraints that are selected for constraint combination are sorted according to their residue range (sort=level), their individual support score (sort=individual), or their residue-wise support score (sort=residue). The input restraints A, B, C and D in the case of 4-to-4 contraint combination are chosen from the first, second, third, and fourth quarter of the sorted list, respectively. In the case of 2-to-1 constraint combination, the restraints A and B are chosen from the first and second half of the sorted list, respectively.
The upper distance bound u of the combined restraint is computed from the upper distance bounds u_1,...,u_n of the restraints that are combined according to the distance parameter:
dsum u = (u_1^-6 + ... + u_n^-6)^(-1/6) d^-6 sum dsumav u = ((u_1^-6 + ... + u_n^-6)/n)^(-1/6)d^-6 d^-6 average dmax u = max(u_1,...,u_n) maximum
Normally, the individual restraints from which combined restraints are formed will be discarded. Optionally, the individual restraints can be kept with a (typically lower) relative weight given by the weightkeep parameter.
Further reading:
- Herrmann et al. J. Mol. Biol. 319, 209-227 (2002).
- Guntert. Meth. Mol. Biol. 278, 353-378 (2004).