文件列表:

Makefile (1805, 2012-10-17)
emd.c (19841, 2012-10-17)
emd.h (1719, 2012-10-17)
emd.i (7397, 2012-10-17)
example1.c (593, 2012-10-17)
example1.py (633, 2012-10-17)
example2.c (755, 2012-10-17)

Earth Mover's Distance Python2 Module ===================================== This module provides a function for computing the [earth mover's distance (EMD)][emd] in [Python2][python]. It wraps [Yossi Rubner's C implementation][rubner_emd] of the EMD into a Python module using a custom [SWIG interface wrapper][swig]. The EMD is a distance measure between two probability distributions. It can be used, for example, to retrieve similar images from a database. However, this implementation is not limited to images or histograms; it can represent distributions over any user-defined features, using any user-defined ground distance. Please see the [original homepage][rubner_emd] for more explanations and references. Installation ------------ Building the module requires the following: - Python2 C headers (`python-dev`) - C compiler and linker, as well as Make (`build-essential`) - [SWIG Simple Wrapper and Interface Generator][swig] (`swig`) - EMD source code and interface definition (`emd.h`, `emd.c`, and `emd.i` in this repository) The name in parentheses after the first three entries is the name of the Debian/Ubuntu Linux package that contains the required files. If all requirements are met, the module can be built using Make. Simply execute `make` in the directory that contains the EMD source code and interface definition. The output should look similar to the following: ~~~~ >>> Building object file 'emd.o'. cc -o emd.o -c emd.c -fPIC -I/usr/include/python2.7 -I/usr/include/python2.7 >>> Generating C interface swig -python emd.i >>> Building object file 'emd_wrap.o'. cc -o emd_wrap.o -c emd_wrap.c -fPIC -I/usr/include/python2.7 -I/usr/include/python2.7 >>> Linking wrapper library '_emd.so'. ld -shared -o _emd.so emd.o emd_wrap.o rm emd_wrap.o emd.o emd_wrap.c ~~~~ You can ignore warnings about redefinitions of `INFINITY` and extra tokens at the end of include statements. If everything went well, the now directory contains the C library `_emd.so` and its Python wrapper `emd.py`. Usage Example ------------- The included `example1.py` is a port of `example1.c`. It demonstrates the basic use of the EMD module. Simply run the script with the Python2 interpreter: ~~~~ $ python2 example1.py 160.542770386 ~~~~ Interface --------- The function `emd` in the `emd` module computes the EMD. (I bet you were surprised by this fact.) It accepts two pairs of feature and weight lists, and a callable for computing the ground distance. ~~~~ from emd import emd print emd( (features1, weights1), (features2, weights2), distance) ~~~~ In above code, `features1` and `features2` are lists of arbitrary Python objects. The implementation invokes the callable `distance` on pairs of feature objects to compute the distance matrix. Each feature object is assigned a weight to characterize the distribution. The implementation treats objects as opaquely as possible. The only limitations are: - `features1` and `weights1` are lists of the same length. The entries of `weights1` must be floating point numbers; `features1` can contain arbitrary objects, but the `distance` function must be able to process them. Similarly for `features2` and `weights2`. - The `distance` argument is a callable object (for example a function) that accepts two arguments (from the `features` lists) and returns a floating point number. See `example1.py` for a filled-in example. Limitations ----------- - The C implementation uses `float` as its fundamental data type for distances and weights. The (typically `double`) floating point objects of Python will be down-cast and lose precision. - See `emd.h` for the hard-coded definitions of maximum signature size, maximum iteration count, and computational constants. - Currently, the wrapper ignores the flow output argument that is available in the C implementation. - The wrapper is *not* suited for concurrent execution. It uses a global variable for the distance callback function, so calling `emd` from concurrent threads will result in undefined behavior. Copyright --------- Only the wrapper code, the Makefile, the Python version of `example1.c`, and this document were written by me and consequently are (c) copyrighted by Peter Dinges. These files are available under the open-source [MIT License][mit-license]. [Yossi Rubner][rubner] is the author of the C code that performs the actual computation. I have included his source code in this repository because I am unsure about the future availability of his homepage. (I could not reach him via email.) [python]: http://python.org/ "Python programming language" [swig]: http://swig.org/ "Simple Wrapper and Interface Generator" [emd]: http://en.wikipedia.org/wiki/Earth_mover's_distance "Explanation of the Earth Mover's Distance" [rubner_emd]: http://ai.stanford.edu/~rubner/emd/default.htm "EMD implementation in C" [rubner]: http://ai.stanford.edu/~rubner/ [mit-license]: http://opensource.org/licenses/mit-license.php

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