Python implementation of EMA, an online multi-class classifier specially suitable for non-stationary problems
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Ema is a supervised-learning algorithm. Concretely, it is an efficient online multiclass classifier which works with a sparse matrix of weights. It is particularly suitable for non-stationary problems. The author of EMA's algorithm is Omid Madani and you can check out the details in:


EMA is implemented both in GNU Octave and in python. However, the python version is the recommended one and the other is left just for a comparison and because it is a conciser version of the algorithm.

  • for (recommended)
  • it is required python 2.7
  • scipy (>= 0.9) (scipy.sparse, specifically)
  • for ema.m you need GNU Octave (tested with v3.2.4)


First you can test that everything works as expected by executing:

> python2.7 ./ test

If everything goes fine, you can install everything with:

> python2.7 ./ install

The setup script allows plenty other options. For help, please consult:

> python2.7 ./ -h

Type of supported input files

  • Greenberg's dataset files (e.g., scientist-17)
  • Encoded Greenberg's dataset file (e.g., scientist-17.sparse). These can be generated from those above using The module can work with any encoding but these are the ones that have been tested on

Execute EMA in Python

For instance, if we want to obtain the R1 and R5 results of scientist-17.sparse we would execute the following:

python2.7 -f scientist-17.sparse

[ 0.30755712 0.54481547]

This can takes from several seconds to a couple of minutes and it outputs the R1 and R5 average values over all the given file. For this concrete example:

  • R1 = 0.30755712
  • R5 = 0.54481547

The module is properly documented and it shows the help of its other arguments by executing:

python2.7 -h

Unit tests can be executed by calling:


Execute EMA in GNU Octave

The octave function (defined in ema.m) requires the dataset already encoded. File *.sparse are already the encoded for such purpose. The encoding is:

<true-class> <number-of-nonzero-features> <indexes-of-nonzero-feature-positions>

For instance, 1 3 1 2 3 specifies that the true class is 1, there are 3 active features (value of 1) that should serve to predict that class, and these features are at the positions 1, 2 and 3.

Encoding Greenberg's dataset files

python2.7 scientist-17 > scientist-17.sparse

The module is properly documented and it shows its help executing:

python2.7 -h

Octave's EMA over an encoded file

Just execute:

octave --eval 'test_ema("scientist-17.sparse");'


R1 = 0.28822

R5 = 0.53427

It will print the R1 and R5 results of the given file.

Right now there is a small discrepancy between the results given by both versions.


Implementer: José Antonio Martín Baena

EMA's author: Omid Madani