Large-scale enumerations and memory problems

*To*: mathgroup at smc.vnet.net*Subject*: [mg35084] Large-scale enumerations and memory problems*From*: "Mark E. Berres" <markb at ravel.zoology.wisc.edu>*Date*: Mon, 24 Jun 2002 03:21:36 -0400 (EDT)*Organization*: University of Wisconsin, Madison*Sender*: owner-wri-mathgroup at wolfram.com

Hi, I am performing some enumerations (v4.1 under Win-XP with 768 MB physical memory and 4GB swap space) with the following simple code: Enum[l_List, (k_Integer)?Positive] := Block[{minusone = Enum[l, k - 1], i, n = Length[l]}, Join @@ Table[(Prepend[#1, l[[i]]] & ) /@ minusone, {i, n}]]. What this does is to take a supplied list of objects, l, and generate all possible combinations of these objects in a string of length k. Thus, even for small l and moderate values of k, the number of combinations becomes very large. I am exporting the results to a file by Export["file.txt", Enum[{G , A , T, C}, 6], "List"] (I want one entry per line of text) but when k becomes "too large", for example if l=4 and k=14, 4^14 = ~268 million, the kernal eventually crashes complaining about memory. I estimated that approx. 1.61 GB is required to store all strings in memory before writing to disk - plenty of room available on my machine, but still it crashes. It appears that the calculation first does its thing and then when initiating a write to disk, crashes. Is there a way to write the results one-at-a-time, rather than the whole-thing-at-once? Or does my problem lie elsewhere? Sincerely, Mark