Mat3 rot3(double theta, Vec3 axis)Returns the matrix representing a rotation by an angle theta (in radians) about a (not necessarily unit) vector axis.
Mat3 rot3_1(Vec3 axis)An alternative version of the above function in which the angle of roation theta is encoded in the length of the vector axis.
void rot3_angle_axis(Mat3 m, double *theta, Vec3 * axis)Sets *theta and *axis to be the angle of rotation and unit vector axis of rotation repectively of the rotation matrix r.