inline btMatrix3x3 evalEulerEqnDeriv(const btVector3& w1, const btVector3& w0, const btScalar dt, const btMatrix3x3 &I) { btMatrix3x3 w1x, Iw1x; const btVector3 Iwi = (I*w1); w1.getSkewSymmetricMatrix(&w1x[0], &w1x[1], &w1x[2]); Iwi.getSkewSymmetricMatrix(&Iw1x[0], &Iw1x[1], &Iw1x[2]); const btMatrix3x3 dfw1 = I + (w1x*I - Iw1x)*dt; return dfw1; }