  We present a new algorithm for an analytic parton shower. While the algorithm
for the final-state shower has been known in the literature, the construction
of an initial-state shower along these lines is new. The aim is to have a
parton shower algorithm for which the full analytic form of the probability
distribution for all branchings is known. For these parton shower algorithms it
is therefore possible to calculate the probability for a given event to be
generated, providing the potential to reweight the event after the simulation.
We develop the algorithm for this shower including scale choices and angular
ordering. Merging to matrix elements is used to describe high-energy tails of
distributions correctly. Finally, we compare our results with those of other
parton showers and with experimental data from LEP, Tevatron and LHC.
