SCODE    		          Copyright (c) 2012-2014 Deniz Yuret

Algorithm: Let X and Y be two categorical variables with finite
cardinalities |X| and |Y|. We observe a set of pairs {xi, yi} drawn
IID from the joint distribution of X and Y. The basic idea behind CODE
and related methods is to represent (embed) each value of X and each
value of Y as points in a common low dimensional Euclidean space such
that values that frequently co-occur lie close to each other. S-CODE
further restricts these points to lie on the unit sphere.  Multi
variable CODE generalizes this idea to more than two variables.
Please see the following papers for a description.

* Amir Globerson, Gal Chechik, Fernando Pereira and Naftali
Tishby. Euclidean Embedding of Co-Occurrence Data. Journal of Machine
Learning Research 8 (Oct), p.2265-2295, 2007.  See Eq. 2, the MM
likelihood which scode maximizes, and Sec. 6.2 for the multivariable
extension.

* Yariv Maron, Michael Lamar, Elie Bienenstock. Sphere Embedding: An
application to unsupervised POS tagging. (NIPS 2010)  See Eq. 10, 11,
12 for the update rule implemented by scode.

* Mehmet Ali Yatbaz, Enis Sert, and Deniz Yuret. 2012. Learning
Syntactic Categories Using Paradigmatic Representations of Word
Context. EMNLP 2012.  Achieves state-of-the-art (80% accuracy) results
in unsupervised part-of-speech induction for English.


Usage: scode [OPTIONS] < file
  file should have columns of arbitrary tokens
  -r RESTART: number of restarts (default 1)
  -i NITER: number of iterations over data (default UINT32_MAX)
  -t THRESHOLD: quit if logL increase for iter <= this (default .001)
  -d NDIM: number of dimensions (default 25)
  -z Z: partition function approximation (default 0.166)
  -p PHI0: learning rate parameter (default 50.0)
  -u ETA0: learning rate parameter (default 0.2)
  -s SEED: random seed (default 0)
  -c calculate real Z (default false)
  -w The first line of the input is weights (default false)
  -v verbose messages (default false)

The input format is:

token1 <tab> token2 <tab> ... token_n <newline>

The output format is:

index:token <tab> count <tab> v1 <tab> v2 <tab> ... v_n <newline>

where index is the column (0, 1, 2, ...) where the token has been
observed, count is the number of times it was observed, and
[v1,v2,...] is its vector embedding.  To compile scode you need the
gsl library.  Otherwise everything is standard C, so just typing make
should give you an executable.


Other executables:

scode-online [options] < file: A complete rewrite of scode to avoid
memory problems with very large datasets.  scode-online performs
vector updates on the fly and does not store the training set in
memory.  The output format is similar to scode.  The gsl dependencies
in the code have been removed, everything is standard C.  Interface
differences with scode: Options like -r, -i, -t does not make sense
and have been removed, scode-online stops and prints its output when
the input runs out.  To simulate -r, run scode-online multiple times
with different seeds.  To simulate -i, feed the training file to stdin
multiple times (see the script "ncat" below).  The counts will be
different from the scode output in this case because scode-online does
not know you are repeating the same data.  Option -c to calculate the
real Z have been removed, use scode-logl for that.  Option -w to give
different weights to different columns have been removed, all weights
are assumed to be 1.  A column in a training file (except the first)
can be empty, in which case it is skipped (empty fields were denoted
with /XX/ in original scode).  To support empty columns the training
file is split strictly at single tab characters (after the last
character of the line, '\n' has been removed).  Multiple tabs denote
multiple empty fields, spaces act as regular data.

ncat 10 file | scode-online > model: ncat writes the file to stdout n
times.  Useful when you want scode-online to go through the training
set multiple times.

scode-logl model < file: Computes the average log-likelihood of the
data in file given the model output by scode or scode-online.  Most of
the computation is performed to calculate the real Z, which takes
about 450 seconds for two columns each with 50K vocabulary.