Re: [Boost-bugs] [Boost C++ Libraries] #7150: What effect does the mean tag have on variance

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #7150: What effect does the mean tag have on variance
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-07-19 01:35:05

#7150: What effect does the mean tag have on variance
-----------------------------------+----------------------------------------
  Reporter:  colmearley@…          |       Owner:  eric_niebler
      Type:  Support Requests      |      Status:  closed      
 Milestone:  To Be Determined      |   Component:  accumulator 
   Version:  Boost 1.49.0          |    Severity:  Problem     
Resolution:  invalid               |    Keywords:              
-----------------------------------+----------------------------------------
Changes (by eric_niebler):

  * status:  new => closed
  * resolution:  => invalid

Comment:

 The
 [http://www.boost.org/doc/libs/1_50_0/doc/html/accumulators/user_s_guide.html#accumulators.user_s_guide.the_statistical_accumulators_library.variance

 docs] make a distinction between `variance` and `lazy_variance`, the
 former depends on `count` and `immediate_mean`, the latter on `moment<2>`
 and `mean`. By telling `variance` to depend instead on `mean`, you've
 changed how the computation is done. You now have a very strange variance
 accumulator that is neither fully immediate nor fully lazy.

 In short: don't do that. :-)

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/7150#comment:1>
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