© 1979 by Institute of Mathematics and its Applications
The Effects of Rounding Error on an Algorithm for Downdating a Cholesky Factorization
Department of Computer Science, University of Maryland
Let the positive definite matrix A have a Cholesky factorizationA = RTR. For a given vector xsuppose that à =A - xxT has a Cholesky factorization à =
T
.This paper considers an algorithm for computing
from R and x and an extension for removing a row from the QR factorization of a regression problem. It is shown that the algorithm is stable in the presence of rounding errors. However, it is also shown that the matrix
can be a very ill-conditioned function of R and x.