[GHC] #7091: DPH Matrix product memory usage

[GHC]

#7091: DPH Matrix product memory usage
--------------------------------------------+---------------------------
        Reporter:  mblanco                  |            Owner:  benl
            Type:  bug                      |           Status:  new
        Priority:  normal                   |        Milestone:  7.8.1
       Component:  Data Parallel Haskell    |          Version:  7.4.1
      Resolution:                           |         Keywords:
Operating System:  Linux                    |     Architecture:  x86
 Type of failure:  Runtime performance bug  |       Difficulty:  Unknown
       Test Case:                           |       Blocked By:
        Blocking:                           |  Related Tickets:
--------------------------------------------+---------------------------

Comment (by George):

 More specifially, in section 5.5 the paper states:

 nested parallelism can increase the asymptotic space complexity
 in a way that this paper does not address [15, 19]. ...
 The flattened version is a hylomorphism that first computes O(n{{{^}}}2)
 distances before reducing them to determine the maximum. Whereas
 the sequential version would run in O(n) space, the flattened version
 needs O(n{{{^}}}2) space to hold the intermediate vector of distances.

 Given the preceding this issue seems to be a known consequence of the dph
 algorithm and as such the status of this should be "Not a bug" as it is
 not a GHC bug. However this is just my opinion and I don't feel I have the
 expertise to actually change the bug status

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7091#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler