Tung-Han Hsieh | PubMed Health

PubMed2003

Neuberger's double-pass algorithm.

We analyze Neuberger's double-pass algorithm for the matrix-vector multiplication R(H) x Y [where R(H) is (n-1,n)th degree rational polynomial of positive definite operator H], and show that the number of floating-point operations is independent of the degree n, provided that the number of sites is much larger than the number of iterations in the conjugate gradient. This implies that the matrix-vector product (H)(-1/2)Y approximately R((n-1,n))(H).Y can be approximated to very high precision with sufficiently large n, without noticeably extra costs. Further, we show that there exists a threshold n(T) such that the double-pass is faster than the single pass for n>n(T), where n(T) approximately 12-25 for most platforms.

Journal Article↗

PubMed2003

Acute aortic dissection associated with left ventricular dysfunction in a postpartum and normotensive young woman.

Aortic dissection is uncommon in young women and is associated with clinical conditions such as pregnancy and Marfan's syndrome. Owing to the low incidence, diagnosis of acute aortic dissection in young women might be missed or delayed in patients who have neither risk factors nor typical clinical manifestations. We report the case of a 28-year-old postpartum woman with aortic dissection. The patient complained of abdominal discomfort, transient back pain, and general malaise at our emergency department 1 week after delivery of a healthy baby. She had no history of hypertension, connective tissue disease or congenital heart disease. Cardiovascular insult was not considered until the patient developed shock. Myocarditis or peripartum cardiomyopathy with left ventricular dysfunction was diagnosed based on imaging studies and cardiac enzyme levels. Finally, computed tomography revealed acute aortic dissection after hemodynamic collapse occurred. This case suggests that acute aortic dissection can be associated with left ventricular dysfunction, and non-specific clinical symptoms in young, normotensive, and postpartum women. A high index of clinical suspicion and alertness are needed to identify this condition.

Acute Disease↗