Re: [tor-bugs] #6232 [Analysis]: Make entropy-over-time graph

["Tor Bug Tracker & Wiki" <torproject-admin@xxxxxxxxxxxxxx>]

#6232: Make entropy-over-time graph
-------------------------+--------------------------------------------------
 Reporter:  arma         |          Owner:              
     Type:  enhancement  |         Status:  needs_review
 Priority:  normal       |      Milestone:              
Component:  Analysis     |        Version:              
 Keywords:               |         Parent:              
   Points:               |   Actualpoints:              
-------------------------+--------------------------------------------------

Comment(by phw):

 A clarification for the math which changed between the initial code and my
 update:

 Assume the early days of Tor, where we have only a few relays in the
 consensus. In fact, it's 7 relays with the following bandwidth:
 `[1, 1, 2, 2, 2, 3, 4]`

 The old code determined the total bandwidth (15, the sum of all bandwidths
 in the list) and calculated:
 `1/15 * log2(1/15) + 1/15 * log2(1/15) + 2/15 * log2(2/15) + 2/15 *
 log2(2/15) + 2/15 * log2(2/15) + 3/15 * log2(3/15) + 4/15 * log2(4/15)`

 The problem is the probabilities. E.g., for the value '1', we expect a
 probability of 2/7 (There are two instances of '1' in all 7 values) and
 not 1/15.

 The uploaded version fixes that. It builds a hash table of the form: `{
 bandwidth_value => observed occurrences }`. Then, it iterates over the
 hash table, adds up the result and we have the entropy.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/6232#comment:9>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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