covsyst_xsect.C:
================
ROOT macro to construct the total systematic 195x195 covariance matrix for
the 3 KLOE cross section measurements KLOE08, KLOE10, KLOE12 from the
individual systematic contributions.

In the SystematicSources/-directory, invoke "root" and then do:

.L covsyst_xsect.C
Xsect()

This will produce a TH2D-root-histogram "hSyst" which contains the total
systematic covariance matrix. It will also output a "KLOE_syst_xsect.dat"-file
of the covariance matrix.

