double Geo_Constraint_Bond(unsigned n, const double *x, double *grad, void *data)
{
int ia, ib, iPos;
double r, r0, g[2][3];
CMol* pMol;
GEO_FIX_BOND *Geo_Fix_r;
Geo_Fix_r = (GEO_FIX_BOND*)data;
pMol = (CMol*)(Geo_Fix_r->pMol);
ia = Geo_Fix_r->ia;
ib = Geo_Fix_r->ib;
r0 = Geo_Fix_r->r0;
if(grad) {
r = pMol->Query_Distance(ia, ib, 1, g);
memset(grad, 0, sizeof(double)*n);
iPos = 3 * ia;
grad[iPos ] = g[0][0];
grad[iPos+1] = g[0][1];
grad[iPos+2] = g[0][2];
iPos = 3 * ib;
grad[iPos ] = g[1][0];
grad[iPos+1] = g[1][1];
grad[iPos+2] = g[1][2];
}
else {
r = pMol->Query_Distance(ia, ib, 0, g);
}
return (r - r0);
}
