restraints dihedral {<restraints-dihedral-statement>} end

<restraints-dihedral-statement> :==

  nassign=<integer>
  --{Required parameter that specifies the maximum expected number
     of assignments. This must be greater than of equal to the actual number.}
  assign <atom-selection> <atom-selection> <atom-selection> <atom-selection>
         <real> <real> <real> <integer>
  --{Assign a dihedral restraint. The 4 number are respectively:
     - force constant in kcal/(mole radians**exponent)
     - equilibrium dihedral value in degrees
     - range around the equilibrium value in degrees
     - exponent for restraint calculation.}
  cv=<integer>
  --{Select partition number for cross-validation.}
  partition=<integer>
  --{Number of partitions for complete cross-validation.}
  scale=<real>
  --{Overall scale factor. Default=1}
  ?
  --{Print a list of current dihedral constraints.}
  reset
  --{Resets the dihedral constraint list.}

  --{The functional form of the restraint is:

     E = constant * well( phi - equilibrium , range )**exponent
     where,
           well(a,b) =    a-b        a >  b
           well(a,b) =     0    -b < a <  b
           well(a,b) =    a+b        a < -b }