Thread: Odd result
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Old 2016-02-04, 13:22   #1
swellman's Avatar
Jun 2012

2,897 Posts
Default Odd result

Lately I have been running the set of xyyx composites through YAFU using the nfs() command in an effort to identify the optimal polys as well as triage the input queue. Have completed several hundred numbers so far, and the results have been great. Sometimes the nfs.job file needs a bit of tweaking but I always end up with a usable poly and parameters. Subsequent test sieving then gives me an estimate for sieving time - a month, a season, two years. But then I encountered something strange (but no crash).

C189_147_41 had a yield of zero in two of the best three polys, and only 1 relation with the best poly. But YAFU was attempting to sieve on the algebraic side. Nothing wrong with that, but obviously something was not right. Once I started test sieving this best poly with the -r flag, all was well - lots of relations were generated at a reasonable speed. Since this best poly matched what my hand calculations showed and I got a reasonable yield on the rational side, I went with it and moved on.

But I thought this number may be an interesting edge case to report. With all three top polys, YAFU seemed to choose the wrong side to sieve, be it -a or -r.

ETA: YAFU v1.34.5 from 2014.

Last fiddled with by swellman on 2016-02-04 at 14:22
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