completed lj parameter set and compute functions for melt example

    def __init__(self):

        self.pmap=dict()

        # coefficients: epsilon, sigma

        self.coeff = {'lj'  : {'lj'  : (1.0,1.0),

                               'NULL': (0.0,1.0)},

                      'NULL': {'lj'  : (0.0,1.0),

                               'NULL': (0.0,1.0)}}

        # set coeffs: eps, sig, 48*eps*sig**12, 24*eps*sig**6,

        #                        4*eps*sig**12,  4*eps*sig**6

        self.coeff = {'lj'  : {'lj'  : (1.0,1.0,48.0,24.0,4.0,4.0),

                               'NULL': (0.0,1.0, 0.0, 0.0,0.0,0.0)},

                      'NULL': {'lj'  : (0.0,1.0, 0.0, 0.0,0.0,0.0),

                               'NULL': (0.0,1.0, 0.0, 0.0,0.0,0.0)}}

    def map_coeff(self,type,name):

    def map_coeff(self,name,type):

        if self.coeff.has_key(name):

           print("map type %d to name %s" % (type,name))

           self.pmap[type] = name

        else:

           print("cannot match atom type",name)

           raise Exception("cannot match atom type %s" % name)

    def compute_force(self,r,itype,jtype,factor_lj):

        return 0.0

    def compute_force(self,rsq,itype,jtype):

        r2inv  = 1.0/rsq

        r6inv  = r2inv*r2inv*r2inv

        lj1 = self.coeff[self.pmap[itype]][self.pmap[jtype]][2]

        lj2 = self.coeff[self.pmap[itype]][self.pmap[jtype]][3]

        return (r6inv * (lj1*r6inv - lj2))

    def compute_energy(self,r,itype,jtype,factor_lj):

        return 0.0

    def compute_energy(self,rsq,itype,jtype):

        r2inv  = 1.0/rsq

        r6inv  = r2inv*r2inv*r2inv

        lj3 = self.coeff[self.pmap[itype]][self.pmap[jtype]][4]

        lj4 = self.coeff[self.pmap[itype]][self.pmap[jtype]][5]

        return (r6inv * (lj3*r6inv - lj4))

lammps_pair_style = LAMMPSLJCutPotential()

print ("lj-melt potential file loaded")