local void sumforces(bodyptr btab, int nbody, bodyptr gtab, int ngrav,
real eps2)
{
bodyptr bp, gp;
double phi0, acc0[NDIM];
vector pos0, dr;
real dr2, dr2i, dr1i, mdr1i, mdr3i;
for (bp = btab; bp < NthBody(btab, nbody); bp = NextBody(bp)) {
phi0 = 0.0;
CLRV(acc0);
SETV(pos0, Pos(bp));
for (gp = gtab; gp < NthBody(gtab, ngrav); gp = NextBody(gp)) {
DOTPSUBV(dr2, dr, Pos(gp), pos0);
dr2i = ((real) 1.0) / (dr2 + eps2);
dr1i = rsqrt(dr2i);
mdr1i = Mass(gp) * dr1i;
mdr3i = mdr1i * dr2i;
phi0 -= mdr1i;
ADDMULVS(acc0, dr, mdr3i);
}
Phi(bp) = phi0;
SETV(Acc(bp), acc0);
}
}
local void sum1force(bodyptr btab, int nbody, int i0, real eps2)
{
bodyptr bp0, bp;
double phi0, acc0[NDIM];
vector pos0, dr;
real dr2, drab, mri, mr3i;
int j;
bp0 = NthBody(btab, i0);
phi0 = 0.0;
CLRV(acc0);
SETV(pos0, Pos(bp0));
for (j = 0; j < nbody; j++)
if (j != i0) {
bp = NthBody(btab, j);
DOTPSUBV(dr2, dr, Pos(bp), pos0);
dr2 += eps2;
drab = rsqrt(dr2);
mri = Mass(bp) / drab;
phi0 -= mri;
mr3i = mri / dr2;
ADDMULVS(acc0, dr, mr3i);
}
Phi(bp0) = phi0;
SETV(Acc(bp0), acc0);
}
local void sumcell(cellptr start, cellptr finish, vector pos0,
real *phi0, vector acc0)
{
real eps2, eps2thrd, dr2, dr2i, dr1i, mdr1i, mdr3i, qdr2, dr5i, phi_q;
vector dr, qdr;
eps2 = eps * eps; // premultiply softening
eps2thrd = eps2 / 3.0; // predivide for soft corr
for (cellptr p = start; p < finish; p++) { // loop over node list
DOTPSUBV(dr2, dr, Pos(p), pos0); // do mono part of force
dr2i = ((real) 1.0) / (dr2 + eps2); // perform only division
dr1i = rsqrt(dr2i); // set inverse soft distance
mdr1i = Mass(p) * dr1i; // form mono potential
mdr3i = mdr1i * dr2i; // get scale factor for dr
DOTPMULMV(qdr2, qdr, Quad(p), dr); // do quad part of force
#if defined(SOFTCORR)
qdr2 -= eps2thrd * Trace(p); // apply Keigo's correction
#endif
dr5i = ((real) 3.0) * dr2i * dr2i * dr1i; // factor 3 saves a multiply
phi_q = ((real) 0.5) * dr5i * qdr2; // form quad potential
mdr3i += ((real) 5.0) * phi_q * dr2i; // adjust radial term
*phi0 -= mdr1i + phi_q; // sum mono and quad pot
ADDMULVS2(acc0, dr, mdr3i, qdr, - dr5i); // sum mono and quad acc
}
}
local void sumnode(cellptr start, cellptr finish,
vector pos0, real *phi0, vector acc0)
{
real eps2, dr2, dr2i, dr1i, mdr1i, mdr3i;
vector dr;
eps2 = eps * eps; // premultiply softening
for (cellptr p = start; p < finish; p++) { // loop over node list
DOTPSUBV(dr2, dr, Pos(p), pos0); // compute sep. vector
// and square of distance
dr2i = ((real) 1.0) / (dr2 + eps2); // perform only division
dr1i = rsqrt(dr2i); // set inverse soft distance
mdr1i = Mass(p) * dr1i; // form partial potential
mdr3i = mdr1i * dr2i; // form scale factor for dr
*phi0 -= mdr1i; // sum potential
ADDMULVS(acc0, dr, mdr3i); // sum acceleration
}
}
local void sumnode(cellptr start, cellptr finish,
vector pos0, real *phi0, vector acc0)
{
cellptr p;
real eps2, dr2, drab, phi_p, mr3i;
vector dr;
eps2 = eps * eps; /* avoid extra multiplys */
for (p = start; p < finish; p++) { /* loop over node list */
DOTPSUBV(dr2, dr, Pos(p), pos0); /* compute separation */
/* and distance squared */
dr2 += eps2; /* add standard softening */
drab = rsqrt(dr2); /* form scalar "distance" */
phi_p = Mass(p) / drab; /* get partial potential */
*phi0 -= phi_p; /* decrement tot potential */
mr3i = phi_p / dr2; /* form scale factor for dr */
ADDMULVS(acc0, dr, mr3i); /* sum partial acceleration */
}
}
local void sumcell(cellptr start, cellptr finish,
vector pos0, real *phi0, vector acc0)
{
cellptr p;
real eps2, dr2, drab, phi_p, mr3i, drqdr, dr5i, phi_q;
vector dr, qdr;
eps2 = eps * eps;
for (p = start; p < finish; p++) { /* loop over node list */
DOTPSUBV(dr2, dr, Pos(p), pos0); /* do mono part of force */
dr2 += eps2;
drab = rsqrt(dr2);
phi_p = Mass(p) / drab;
mr3i = phi_p / dr2;
DOTPMULMV(drqdr, qdr, Quad(p), dr); /* do quad part of force */
dr5i = ((real) 1.0) / (dr2 * dr2 * drab);
phi_q = ((real) 0.5) * dr5i * drqdr;
*phi0 -= phi_p + phi_q; /* add mono and quad pot */
mr3i += ((real) 5.0) * phi_q / dr2;
ADDMULVS2(acc0, dr, mr3i, qdr, -dr5i); /* add mono and quad acc */
}
}
