Changes between Version 4 and Version 10 of Ticket #10735
 Timestamp:
 Feb 15, 2014, 12:56:54 PM (9 years ago)
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Ticket #10735

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Summary
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Simon 2descent may not check for solubility at archimedean places.
toSimon 2descent only returns an upper bound on the 2Selmer rank

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to
#11005

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Milestone
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sage5.12
tosage6.2

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Ticket #10735 – Description
v4 v10 4 4 5 5 Sometimes the second entry is larger than the actual 2Selmer rank as computed by mwrank, and predicted by BSD. The first curve I know of for which this happens is the elliptic curve '438e1' from Cremona's tables. 6 7 This curve definitely possesses 2covers which are everywhere locally soluble EXCEPT at that infinite place. These probably explain the discrepancy.8 6 9 7 {{{ … … 16 14 1 17 15 }}} 16 17 The explanation for this is that `E.simon_two_descent()`, unlike Cremona's `mwrank`, does not do a second descent and therefore only determines an upper bound on the 2Selmer rank.