Python interface
Seldon comes with a Python interface generated by Swig. In Seldon 5.0, the interface is limited: it only contains one vector structure (full vector, double precision) and one matrix structure (full row-major matrix, double precision). Extending the interface is easy, so a more complete interface is planned for version 5.1.
This page only addresses the compilation and the use of the interface under Linux. The generation of the interface was not tested on another platform yet. No known issue should prevent the interface from running successfully on another platform.
Compiling the interface
In addition to a C++ compiler, one needs Swig 1.3.x. Swig 1.1 cannot generate the interface. You will also need Python (say, 2.5 or 2.6, but previous versions should work too) and its headers.
In Seldon directory (root), you may simply launch scons if you
have SCons installed (version
>=1.0). You may also execute lines similar to those launched by SCons:
$ g++ -o Seldon.os -c -fPIC -DSELDON_DEBUG_LEVEL_4 \ -I/usr/include/python2.6 Seldon.cpp $ swig -o seldon_wrap.cc -Wall -c++ -python seldon.i $ g++ -o seldon_wrap.os -c -fPIC -DSELDON_DEBUG_LEVEL_4 \ -I/usr/include/python2.6 seldon_wrap.cc $ g++ -o _seldon.so -shared Seldon.os seldon_wrap.os
This should generate the Python module seldon.py and the
shared library _seldon.so. You may want to place these two files
in a directory of your $PYTHONPATH, where Python searches for
modules (in addition to the local directory .).
Using the interface
In Seldon directory (root), or in any place if seldon.py and
_seldon.so are in a directory of $PYTHONPATH, you
may launch Python and load the module.
It is recommended to use IPython instead of the regular Python shell, for convenience:
$ ls SConstruct Seldon.hxx SeldonHeader.hxx _seldon.so computation/ Seldon.cpp Seldon.os SeldonSolver.hxx array3d/ license matrix/ seldon.i seldon_wrap.cc share/ vector/ matrix_sparse/ seldon.py seldon_wrap.os test/ version $ ipython Python 2.6.2 (release26-maint, Apr 19 2009, 01:58:18) Type "copyright", "credits" or "license" for more information. IPython 0.9.1 -- An enhanced Interactive Python. ? -> Introduction and overview of IPython's features. %quickref -> Quick reference. help -> Python's own help system. object? -> Details about 'object'. ?object also works, ?? prints more. In [1]: import seldon In [2]:
The module mainly provides VectorDouble and
MatrixDouble. The former is the same as Vector<double,
VectFull> and the latter is the same as Matrix<double,
General, RowMajor>. Essentially all methods of these two classes are
available. Example with VectorDouble:
In [1]: import seldon In [2]: x = seldon.VectorDouble(5) In [3]: x.Fill() In [4]: x.Print() 0 1 2 3 4 In [5]: x.Reallocate(2) In [6]: x.Print() 0 1
Example with MatrixDouble:
In [1]: from seldon import * In [2]: M = MatrixDouble(3, 3) In [3]: M.SetIdentity() In [4]: M.Print() 1 0 0 0 1 0 0 0 1 In [5]: M.GetM() Out[5]: 3 In [6]: M.GetM() * M.GetN() Out[6]: 9
The main difference lies in the access operator: it is []
instead of (), to be consistent with NumPy conventions:
In [1]: import seldon In [2]: x = seldon.VectorDouble(3) In [3]: x[0] = 2.; x[1] = -1.; x[2] = 10. In [4]: x.Print() 2 -1 10 In [5]: M = seldon.MatrixDouble(3, 3) In [6]: M.SetIdentity() In [7]: M[1, 0] = -5 In [8]: M.Print() 1 0 0 -5 1 0 0 0 1 In [8]: M[2, 2] + x[0] Out[9]: 3.0
C++ exceptions are converted to Python exceptions:
In [2]: x = seldon.VectorDouble(3) In [3]: x[3] = 2. --------------------------------------------------------------------------- Exception Traceback (most recent call last) /home/mallet/src/seldon/in () /home/mallet/src/seldon/seldon.pyc in __setitem__(*args) 1091 def Read(*args): return _seldon.VectorDouble_Read(*args) 1092 def __getitem__(*args): return _seldon.VectorDouble___getitem__(*args) -> 1093 def __setitem__(*args): return _seldon.VectorDouble___setitem__(*args) 1094 def __len__(*args): return _seldon.VectorDouble___len__(*args) 1095 VectorDouble_swigregister = _seldon.VectorDouble_swigregister Exception: ERROR! Index out of range in Vector ::operator(). Index should be in [0, 2], but is equal to 3.
You can convert a vector or a matrix to a NumPy array:
In [1]: import seldon
In [2]: import numpy
In [3]: M = seldon.MatrixDouble(3, 3)
In [4]: M.Fill()
In [5]: M = numpy.array(M)
In [6]: M.shape
Out[6]: (3, 3)
In [7]: M
Out[7]:
array([[ 0., 1., 2.],
[ 3., 4., 5.],
[ 6., 7., 8.]])
In [8]: M.sum()
Out[8]: 36.0
