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hdyn_flat.C

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//
//  hdyn_flat.C: functions related to orbit integration within the hdyn class.
//                   - member functions for FLAT trees only
//.............................................................................
//    version 1:  Jul 1996   Steve McMillan
//    version 2:
//.............................................................................

#include "hdyn.h"

//-----------------------------------------------------------------------------
//  flat_accumulate_acc_and_jerk -- calculates the contribution to the
//                                  acceleration & jerk on this node from
//                                  the node leaf.
//                                  note: for flat trees only
//-----------------------------------------------------------------------------

inline void
hdyn::flat_accumulate_acc_and_jerk(hdyn * leaf,    // attracting leaf node
                                   real eps2)      // softening length squared
{
    vector d_pos = leaf->get_pred_pos() - get_pred_pos();
    vector d_vel = leaf->get_pred_vel() - get_pred_vel();
    real r2inv = 1.0 / (d_pos * d_pos + eps2);
    real a3 = -3.0 * (d_pos * d_vel) * r2inv;
    real mrinv = leaf->get_mass() * sqrt(r2inv);
    pot -= mrinv;
    real mr3inv = mrinv * r2inv;
    acc += mr3inv * d_pos;
    jerk += mr3inv * (d_vel + a3 * d_pos);
}

//-----------------------------------------------------------------------------
//  flat_calculate_acc_and_jerk -- calculates acceleration & jerk on this node:
//                                 from all nodes under p (if p is root ptr);
//                                 or from the node p (if p is a leaf ptr).
//
//                                 NOTE: for flat trees only
//
//-----------------------------------------------------------------------------

#ifdef RECURSIVE_LOOP

void hdyn::flat_calculate_acc_and_jerk(hdyn * p,    // root or leaf
                                       real eps2)   // softening length squared
{
    if (p->is_root()) {                 // p is root, so
                                        // invoke for all leaves
        for_all_daughters(hdyn, p, d)   
            flat_calculate_acc_and_jerk(d, eps2);

    } else {                            // p is leaf, but
                                        // not this leaf
        if (p != this)
            flat_accumulate_acc_and_jerk(p, eps2);
    }
}

#else

// Looping by recursion (as above) is relatively expensive on many systems.
// Remove the recursion for the sake of efficiency (and readability?) by
// using an explicit loop.

void hdyn::flat_calculate_acc_and_jerk(hdyn * p,    // root or leaf
                                       real eps2)   // softening length squared
{
    if (p->is_root()) {                 // p is root, so
                                        // invoke for all leaves
        for_all_daughters(hdyn, p, d)   
            if (d != this)
                flat_accumulate_acc_and_jerk(d, eps2);

    } else {                            // NOTE: else clause currently not used

        if (p != this)
            flat_accumulate_acc_and_jerk(p, eps2);

    }
}

#endif

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