quaternion integration in ESyS-Particle

Dear all,

I have a trouble understanding the quaternion integration algorithm in ESyS. I read the rotParticle.cpp file, that:

    // integrate rotational part
    m_angVel += (dt*m_div_inertRot) * m_moment;
    m_quat += (dt/2.0)*(Quaternion(0, m_angVel)*m_quat);

I can understand the first line to integrate the anglar velocity, while I cannot understand how to get the second line. Could anybody kindly explain the second line to me? It is really hard to understand quaternion integrations.

By the way, for the algorithm, is there any paper or book I can refer to?

Thank you very much.

Best regards,

Aaron