A LINPACK-style condition estimator for the equationAX-XB^{T} = C

Estimation of the condition number of
AX- XB^{T} = C
requires an approximation of the smallest l
2
singular value of the linear transformation
X \rightarrow AX - XB^{T}
. The approximation is obtained from a step of inverse iteration applied to a heuristically chosen starting matrix. In the style of LINPACK, the cost of the estimator is kept down by using the same matrix factorizatlons to make the estimate as are used to solve
AX - XB^{T} = C
. Computational experiments verify its reliability.