static private void vp(List <Body> bv, int nstep)
{
MathVector dacc = MathVector.makeMathVector();
MathVector dvel = MathVector.makeMathVector();
double dthf = 0.5 * BH.DTIME;
for (int i = 0; i < bv.Count; ++i)
{
Body b = bv[i];
MathVector acc1 = b.newAcc.cloneMathVector();
if (nstep > 0)
{
dacc.subtraction2(acc1, b.acc);
dvel.multScalar2(dacc, dthf);
dvel.addition(b.vel);
b.vel = dvel.cloneMathVector();
}
b.acc = acc1.cloneMathVector();
dvel.multScalar2(b.acc, dthf);
MathVector vel1 = b.vel.cloneMathVector();
vel1.addition(dvel);
MathVector dpos = vel1.cloneMathVector();
dpos.multScalar1(BH.DTIME);
dpos.addition(b.pos);
b.pos = dpos.cloneMathVector();
vel1.addition(dvel);
b.vel = vel1.cloneMathVector();
}
}
/**
* 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);
}