Low red-shift formula for the luminosity distance in a LTB model with
  cosmological constant
  We calculate the low red-shift Taylor expansion for the luminosity distance
for an observer at the center of a spherically symmetric matter inhomogeneity
with a non vanishing cosmological constant. We then test the accuracy of the
formulas comparing them to the numerical calculation for different cases for
both the luminosity distance and the radial coordinate. The formulas can be
used as a starting point to understand the general non linear effects of a
local inhomogeneity in presence of a cosmological constant, without making any
special assumption about the inhomogeneity profile.
