qS2
q = one + z * (qS1 + z * (qS2 + z * (qS3 + z * qS4)));
q = one + z * (qS1 + z * (qS2 + z * (qS3 + z * qS4)));
q = one + z * (qS1 + z * (qS2 + z * (qS3 + z * qS4)));
q = one + t * (qS1 + t * (qS2 + t * (qS3 + t * qS4)));
q = one + t * (qS1 + t * (qS2 + t * (qS3 + t * qS4)));