I should warn you right from the beginning
that the algorithm used in GraphEnt is neither the most stable nor the
most efficient of those published3 (but it is the one that is the easiest to code). Additionally, for those
cases where the calculation includes a known figure-of-merit for the phase angles, GraphEnt is
performing additional approximations which although I hope that
are generally safe, they do not represent
the best that can be achieved with the data (see pages and
).
I should also warn you that the amount of time that the calculation may require depends on the
input data quality
and there is no a priori guarantee that the given algorithm will converge
even if given enough time. Having said that, a 262144 (=128x64x32) pixels
GraphEnt
mFoexp(i)
map corresponding to a reasonably accurate data set could be calculated in less than
8 minutes of CPU time on a DEC Alpha 1200, and a 524288 (=128x128x32) pixels GraphEnt difference Patterson map for a loosy derivative (which makes the calculation easy)
took only 46 seconds on the same machine. Finally, a 2Å
(2mFo - DFc)exp(i
) synthesis with
3072000 (=160x160x120) pixels took
40min.