reduceOverParticles
auto kinEnergy = ps.reduceOverParticles(.., SUM, [&](auto p_idx)
{return 0.5_r * ac.getMass(p_idx) * ac.getLinearVelocity(p_idx) * ac.getLinearVelocity(p_idx);});
auto kinEnergy = ps.reduceOverParticles(.., SUM, [&](auto p_idx)
{return 0.5_r * ac.getMass(p_idx) * ac.getLinearVelocity(p_idx) * ac.getLinearVelocity(p_idx);});