Message1393

Author malte
Recipients emilkeyder, erez, malte, rpgoldman, silvia
Date 2011-06-29.18:41:03
Content
When working on issue240, I think I found a bug with the landmark heuristic.
Here is what Robert and Tony tried to do (after translate/preprocess, and using
debug mode; paste command as a single line):

$ make debug && ./downward-1-debug --heuristic
"hlm,hff=lm_ff_syn(lm_rhw(reasonable_orders=true,cost_type=2,lm_cost_type=2))"
--search "lazy_greedy([hlm,hff], preferred=[hlm,hff])" < output

This fails noting that the search space was exhausted. However, when using just
hff (e.g. change "[hlm,hff]" to "[hff]" in both places), the problem is solved,
hinting at wrong dead-ends reported by h^LM.

The problem also appears when using the plain LM heuristic in various forms.
Here are some simple examples:

$ ./downward-1-debug --search 'astar(blind())' < output
=> Solves the task.

$ ./downward-1-debug --search 'astar(lmcount(lm_rhw(reasonable_orders=false)))'
< output
=> Exhausts the search space.

$ ./downward-1-debug --search 'astar(lmcount(lm_hm(m=1)))' < output
=> LM construction claims problem is unsolvable.

$ ./downward-1-debug --search 'astar(lmcount(lm_zg()))' < output
=> LM construction assert-fails.

Possibly a clue, possibly not: Disabling all orderings in LM_RHW leads to the
problem being solved:
$ ./downward-1-debug --search
'astar(lmcount(lm_rhw(reasonable_orders=false,no_orders=true)))' < output

However, this doesn't help with the other LM generation methods, which already
fail during LM graph construction.
History
Date User Action Args
2011-06-29 18:41:04maltesetmessageid: <1309365664.21.0.230432052802.issue247@gmail.com>
2011-06-29 18:41:04maltesetrecipients: + malte, erez, silvia, emilkeyder, rpgoldman
2011-06-29 18:41:04maltelinkissue247 messages
2011-06-29 18:41:03maltecreate