R help - Mar 2012 - [slightly OT] le: will a new point shift the solution question

Hello,

Is there an R function that given a linear regression solution for a data set
will answer in the most efficient way whether a new data point shifts the
solution or not? or whether the new solution would differ by less than some
error.

I need this in the context of an iterative method and such a function would
spare a lot of time.

The closest answer I can find to this, involves keeping track of the QR and
updating it with a row append. I would like to only get a boolean answer because
a 'no' answer would spare tons of flops.

Many thanks in advance,
Best regards,
Giovanni