/** * Evaluate gravitational field on the body. * The original olden version calls a routine named "walkscan", * but we use the same name that is in the Barnes code. */ public void hackGravity(double rsize, Node root) { MathVector pos0 = pos.cloneMathVector(); HG hg = HG.makeHG(this, pos); hg = root.walkSubTree(rsize * rsize, hg); phi = hg.phi0; newAcc = hg.acc0; }