eflomal

Efficient Low-Memory Aligner

This work is a fork of Robert Ösling's eflomal with a few fixes and additional features:

• when builing on Mac OS, remove -lrt from LDFLAGS
• add mkmodel.py script for computing translation probabilities directly from a parallel corpus; this first computes alignment using eflomal then derives probabilities from it

eflomal is a word alignment tool based on efmaral, with the following main differences:

• More compact data structures are used, so memory requirements are much lower (by orders of magnitude).
• The estimation of alignment variable marginals is done one sentence at a time, which also saves a lot of memory at no detectable cost in accuracy.

Technical details relevant to both efmaral and eflomal can be found in the following article:

• Östling and Tiedemann (2016) (BibTeX).

Installing

To compile and install the C binary and the Python bindings:

make
sudo make install
python3 setup.py install

edit Makefile manually if you want to install somewhere other than the default /usr/local/bin. Note that the align.py script now uses the eflomal executable in the same directory as align.py, rather than in $PATH.

On mac you will need to compile using gcc because clang does not support openmp:

    brew install gcc
    export CC=/usr/local/bin/gcc-8

Change CC to match your settings if necessary. Then proceed to build and install normally.

Using

There are three main ways of using eflomal:

1. Directly call the eflomal binary. Note that this requires some preprocessing.
2. Use the align.py command-line interface, which is partly compatible with that of efmaral. Run python3 align.py --help for instructions.
3. Use the Cython module to call the eflomal binary, this takes care of the preprocessing and file conversions necessary. See the docstrings in eflomal.pyx for documentation.

In addition, there are convenience scripts for aligning and symmetrizing (with the atools program from fast_align) as well as evaluating with data from the WPT shared task datasets. These work the same way as in efmaral, please see its README for details.

Data format

The align.py interface expects one sentence per line with space-separated tokens, similar to most word alignment software.

Performance

This is a comparison between eflomal, efmaral and fast_align.

The difference between efmaral and eflomal is in part due to different default parameters, in particular the number of iterations and the number of independent samplers.

Note that all timing figures below include alignments in both directions (run in parallel) and symmetrization.

eflomal

Languages	Sentences	AER	CPU time (s)	Real time (s)
English-French	1,130,551	0.081	1,232	337
English-Inkutitut	340,601	0.203	161	44
Romanian-English	48,681	0.298	159	33
English-Hindi	3,530	0.467	31	6

efmaral

Languages	Sentences	AER	CPU time (s)	Real time (s)
English-Swedish	1,862,426	0.133	1,719	620
English-French	1,130,551	0.085	763	279
English-Inkutitut	340,601	0.235	122	46
Romanian-English	48,681	0.287	161	46
English-Hindi	3,530	0.483	98	10

fast_align

Languages	Sentences	AER	CPU time (s)	Real time (s)
English-Swedish	1,862,426	0.205	11,090	672
English-French	1,130,551	0.153	3,840	241
English-Inuktitut	340,601	0.287	477	47
Romanian-English	48,681	0.325	208	17
English-Hindi	3,530	0.672	24	2