/**
* Decide if the cell is too close to accept as a single term.
*
* @return true if the cell is too close.
*/
public bool subdivp(double dsq, HG hg)
{
MathVector dr = MathVector.makeMathVector();
dr.subtraction2(pos, hg.pos0);
double drsq = dr.dotProduct();
// in the original olden version drsp is multiplied by 1.0
return(drsq < dsq);
}
/**
* Compute a single body-body or body-cell interaction
*/
public HG gravSub(HG hg)
{
MathVector dr = MathVector.makeMathVector();
dr.subtraction2(pos, hg.pos0);
double drsq = dr.dotProduct() + (EPS * EPS);
double drabs = Math.Sqrt(drsq);
double phii = mass / drabs;
hg.phi0 -= phii;
double mor3 = phii / drsq;
dr.multScalar1(mor3);
hg.acc0.addition(dr);
return(hg);
}