Zero probability mass in sampler

[fritzo]

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Testing h4
cd /home/fritz/pomagma/data/test/debug/atlas/h4

POMAGMA_SIZE=127 \
  POMAGMA_LOG_FILE=/home/fritz/pomagma/data/test/debug/atlas/h4/test.log \
  POMAGMA_LOG_LEVEL=2 \
  /home/fritz/pomagma/build/debug/src/surveyor/h4.init \
  /home/fritz/pomagma/data/test/debug/atlas/h4/0.h5 \
  /home/fritz/pomagma/pomagma/theory/h4.compiled \
  /home/fritz/pomagma/pomagma/language/h4.language \
  8
# took 0.231 sec
POMAGMA_LOG_FILE=/home/fritz/pomagma/data/test/debug/atlas/h4/test.log \
  POMAGMA_LOG_LEVEL=2 \
  /home/fritz/pomagma/build/debug/src/cartographer/cartographer \
  /home/fritz/pomagma/data/test/debug/atlas/h4/0.h5 \
  /home/fritz/pomagma/pomagma/theory/h4.compiled \
  /home/fritz/pomagma/pomagma/language/h4.language \
  ipc:///home/fritz/pomagma/data/test/debug/atlas/h4/cartographer.socket
connecting to cartographer at ipc:///home/fritz/pomagma/data/test/debug/atlas/h4/cartographer.socket
# took 0.239 sec
POMAGMA_SIZE=191 \
  POMAGMA_LOG_FILE=/home/fritz/pomagma/data/test/debug/atlas/h4/test.log \
  POMAGMA_LOG_LEVEL=2 \
  /home/fritz/pomagma/build/debug/src/surveyor/h4.survey \
  /home/fritz/pomagma/data/test/debug/atlas/h4/1.h5 \
  /home/fritz/pomagma/data/test/debug/atlas/h4/2.h5 \
  /home/fritz/pomagma/pomagma/theory/h4.compiled \
  /home/fritz/pomagma/pomagma/language/h4.language \
  8
# took 0.111 sec

==== LOG FILE ====
21836   0.073636    INFO    Validating disjoint pair of BinaryRelations
21836   0.084774    INFO    Validating Sampler
21836   0.084801    INFO    starting 8 survey threads
21836   0.085053    ERROR   zero probability mass
    /home/fritz/pomagma/include/pomagma/platform/sampler_impl.hpp : 198
    pomagma::Sampler::Arity pomagma::Sampler::BoundedSampler::sample_arity(pomagma::rng_t&) const