Generic discrete_log
 
  
 
  
 
 
 
 
 
 
    
        
        asked 7 years ago  
 
 kdr gravatar image  
 
 
 
 
    
        
        updated 4 years ago  
 
 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 (
    
        7 years ago
    )
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