X-PLOR provides a means to restrain the main coordinate set ( atom properties x,y,z) to the reference coordinate set ( atom properties refx, refy, refz). The restraints are defined as
where the sum extends over all atoms, 
is individual weights,
is the atomic coordinates of the main set, 
is
the atomic coordinates of the reference set, and e is an
exponent. The individual weights 
correspond to
the atom property HARM and can be assigned
using the vector statement
(Section 2.16); the physical dimension of HARM is
kcal mole
Å
. By default, 
is zero. The
reference coordinate set can be assigned using the
vector statement or by using the DISPosition option of
the coordinate statement. The exponent e is set
by using the restraints harmonic statement.
