A word of caution

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.

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 262,144 (=128x64x32) pixels GraphEnt mF_oexp(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, a 524,288 (=128x128x32) pixels GraphEnt difference Patterson map for a loosy derivative (which makes the calculation easy) took only 46 seconds on the same machine, and a 2Å (2mF_o - DF_c)exp(i) synthesis with 3,072,000 (=160x160x120) pixels took 40min. Finally, a 2-0.8Å (2F_o - F_c)exp(i) synthesis with 9,437,184 (=192x256x192) pixels for a 4--helical bundle protein took only 13 minutes on a Pentium 800MHz (but the data were, of course, rather weak at this resolution range).

Footnotes

... published³

See for example Maximum Entropy and Bayesian Methods in Inverse Problems (1985), edited by Smith, C.R. & Grandy, W.T., Jr., Dordrecht : Reidel.