  Let R be a discrete valuation ring (DVR) and K be its fraction field. If M is
a matrix over R admitting a LU decomposition, it could happen that the entries
of the factors L and U do not lie in R, but just in K. Having a good control on
the valuations of these entries is very important for algorithmic applications.
In the paper, we prove that in average these valuations are not too large and
explain how one can apply this result to provide an efficient algorithm
computing a basis of a coherent sheaf over A^1 from the knowledge of its
stalks.
