Generic discrete_log

asked 2017-06-18 02:11:41 +0100

kdr gravatar image

updated 2020-06-09 22:01:51 +0100

FrédéricC gravatar image

I've been struggling with discrete_log function. The docs say it is the generic BSGS algorithm that is supposed to work in any group. The function works e.g. if I write

discrete_log(Mod(9, 17), Mod(2, 17), 16, operation='*')

However it keeps returning 0 when I put operation='other', e.g.

discrete_log(9, 2, 16, operation='other', op=lambda x, y: (x * y) % 17)

The op function is not even called once. Is there something that I'm doing wrong or is discrete_log not really generic?

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For my version 7.5.1 the first line does not work,

sage: discrete_log(Mod(9, 17), Mod(2, 17), 16, operation='*')

runs into 

ValueError: No discrete log of 9 found to base 2

However...

sage: discrete_log(Mod(9, 17), Mod(2, 17), 8, operation='*')
7

Typing ??discrete_log i could not find the path really considering the 'other' operation... So why not use the operations * and + available? (Or write the corresponding adapted code to search for the discrete log in a very special situation...)

dan_fulea gravatar imagedan_fulea ( 2017-06-18 17:50:08 +0100 )edit
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