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.. _sphx_glr_auto_examples_plot_gromov_barycenter.py:
=====================================
Gromov-Wasserstein Barycenter example
=====================================
This example is designed to show how to use the Gromov-Wasserstein distance
computation in POT.
.. code-block:: python
# Author: Erwan Vautier <erwan.vautier@gmail.com>
# Nicolas Courty <ncourty@irisa.fr>
#
# License: MIT License
import numpy as np
import scipy as sp
import scipy.ndimage as spi
import matplotlib.pylab as pl
from sklearn import manifold
from sklearn.decomposition import PCA
import ot
Smacof MDS
----------
This function allows to find an embedding of points given a dissimilarity matrix
that will be given by the output of the algorithm
.. code-block:: python
def smacof_mds(C, dim, max_iter=3000, eps=1e-9):
"""
Returns an interpolated point cloud following the dissimilarity matrix C
using SMACOF multidimensional scaling (MDS) in specific dimensionned
target space
Parameters
----------
C : ndarray, shape (ns, ns)
dissimilarity matrix
dim : int
dimension of the targeted space
max_iter : int
Maximum number of iterations of the SMACOF algorithm for a single run
eps : float
relative tolerance w.r.t stress to declare converge
Returns
-------
npos : ndarray, shape (R, dim)
Embedded coordinates of the interpolated point cloud (defined with
one isometry)
"""
rng = np.random.RandomState(seed=3)
mds = manifold.MDS(
dim,
max_iter=max_iter,
eps=1e-9,
dissimilarity='precomputed',
n_init=1)
pos = mds.fit(C).embedding_
nmds = manifold.MDS(
2,
max_iter=max_iter,
eps=1e-9,
dissimilarity="precomputed",
random_state=rng,
n_init=1)
npos = nmds.fit_transform(C, init=pos)
return npos
Data preparation
----------------
The four distributions are constructed from 4 simple images
.. code-block:: python
def im2mat(I):
"""Converts and image to matrix (one pixel per line)"""
return I.reshape((I.shape[0] * I.shape[1], I.shape[2]))
square = spi.imread('../data/square.png').astype(np.float64)[:, :, 2] / 256
cross = spi.imread('../data/cross.png').astype(np.float64)[:, :, 2] / 256
triangle = spi.imread('../data/triangle.png').astype(np.float64)[:, :, 2] / 256
star = spi.imread('../data/star.png').astype(np.float64)[:, :, 2] / 256
shapes = [square, cross, triangle, star]
S = 4
xs = [[] for i in range(S)]
for nb in range(4):
for i in range(8):
for j in range(8):
if shapes[nb][i, j] < 0.95:
xs[nb].append([j, 8 - i])
xs = np.array([np.array(xs[0]), np.array(xs[1]),
np.array(xs[2]), np.array(xs[3])])
Barycenter computation
----------------------
.. code-block:: python
ns = [len(xs[s]) for s in range(S)]
n_samples = 30
"""Compute all distances matrices for the four shapes"""
Cs = [sp.spatial.distance.cdist(xs[s], xs[s]) for s in range(S)]
Cs = [cs / cs.max() for cs in Cs]
ps = [ot.unif(ns[s]) for s in range(S)]
p = ot.unif(n_samples)
lambdast = [[float(i) / 3, float(3 - i) / 3] for i in [1, 2]]
Ct01 = [0 for i in range(2)]
for i in range(2):
Ct01[i] = ot.gromov.gromov_barycenters(n_samples, [Cs[0], Cs[1]],
[ps[0], ps[1]
], p, lambdast[i], 'square_loss', # 5e-4,
max_iter=100, tol=1e-3)
Ct02 = [0 for i in range(2)]
for i in range(2):
Ct02[i] = ot.gromov.gromov_barycenters(n_samples, [Cs[0], Cs[2]],
[ps[0], ps[2]
], p, lambdast[i], 'square_loss', # 5e-4,
max_iter=100, tol=1e-3)
Ct13 = [0 for i in range(2)]
for i in range(2):
Ct13[i] = ot.gromov.gromov_barycenters(n_samples, [Cs[1], Cs[3]],
[ps[1], ps[3]
], p, lambdast[i], 'square_loss', # 5e-4,
max_iter=100, tol=1e-3)
Ct23 = [0 for i in range(2)]
for i in range(2):
Ct23[i] = ot.gromov.gromov_barycenters(n_samples, [Cs[2], Cs[3]],
[ps[2], ps[3]
], p, lambdast[i], 'square_loss', # 5e-4,
max_iter=100, tol=1e-3)
Visualization
-------------
The PCA helps in getting consistency between the rotations
.. code-block:: python
clf = PCA(n_components=2)
npos = [0, 0, 0, 0]
npos = [smacof_mds(Cs[s], 2) for s in range(S)]
npost01 = [0, 0]
npost01 = [smacof_mds(Ct01[s], 2) for s in range(2)]
npost01 = [clf.fit_transform(npost01[s]) for s in range(2)]
npost02 = [0, 0]
npost02 = [smacof_mds(Ct02[s], 2) for s in range(2)]
npost02 = [clf.fit_transform(npost02[s]) for s in range(2)]
npost13 = [0, 0]
npost13 = [smacof_mds(Ct13[s], 2) for s in range(2)]
npost13 = [clf.fit_transform(npost13[s]) for s in range(2)]
npost23 = [0, 0]
npost23 = [smacof_mds(Ct23[s], 2) for s in range(2)]
npost23 = [clf.fit_transform(npost23[s]) for s in range(2)]
fig = pl.figure(figsize=(10, 10))
ax1 = pl.subplot2grid((4, 4), (0, 0))
pl.xlim((-1, 1))
pl.ylim((-1, 1))
ax1.scatter(npos[0][:, 0], npos[0][:, 1], color='r')
ax2 = pl.subplot2grid((4, 4), (0, 1))
pl.xlim((-1, 1))
pl.ylim((-1, 1))
ax2.scatter(npost01[1][:, 0], npost01[1][:, 1], color='b')
ax3 = pl.subplot2grid((4, 4), (0, 2))
pl.xlim((-1, 1))
pl.ylim((-1, 1))
ax3.scatter(npost01[0][:, 0], npost01[0][:, 1], color='b')
ax4 = pl.subplot2grid((4, 4), (0, 3))
pl.xlim((-1, 1))
pl.ylim((-1, 1))
ax4.scatter(npos[1][:, 0], npos[1][:, 1], color='r')
ax5 = pl.subplot2grid((4, 4), (1, 0))
pl.xlim((-1, 1))
pl.ylim((-1, 1))
ax5.scatter(npost02[1][:, 0], npost02[1][:, 1], color='b')
ax6 = pl.subplot2grid((4, 4), (1, 3))
pl.xlim((-1, 1))
pl.ylim((-1, 1))
ax6.scatter(npost13[1][:, 0], npost13[1][:, 1], color='b')
ax7 = pl.subplot2grid((4, 4), (2, 0))
pl.xlim((-1, 1))
pl.ylim((-1, 1))
ax7.scatter(npost02[0][:, 0], npost02[0][:, 1], color='b')
ax8 = pl.subplot2grid((4, 4), (2, 3))
pl.xlim((-1, 1))
pl.ylim((-1, 1))
ax8.scatter(npost13[0][:, 0], npost13[0][:, 1], color='b')
ax9 = pl.subplot2grid((4, 4), (3, 0))
pl.xlim((-1, 1))
pl.ylim((-1, 1))
ax9.scatter(npos[2][:, 0], npos[2][:, 1], color='r')
ax10 = pl.subplot2grid((4, 4), (3, 1))
pl.xlim((-1, 1))
pl.ylim((-1, 1))
ax10.scatter(npost23[1][:, 0], npost23[1][:, 1], color='b')
ax11 = pl.subplot2grid((4, 4), (3, 2))
pl.xlim((-1, 1))
pl.ylim((-1, 1))
ax11.scatter(npost23[0][:, 0], npost23[0][:, 1], color='b')
ax12 = pl.subplot2grid((4, 4), (3, 3))
pl.xlim((-1, 1))
pl.ylim((-1, 1))
ax12.scatter(npos[3][:, 0], npos[3][:, 1], color='r')
.. image:: /auto_examples/images/sphx_glr_plot_gromov_barycenter_001.png
:align: center
**Total running time of the script:** ( 0 minutes 5.906 seconds)
.. only :: html
.. container:: sphx-glr-footer
.. container:: sphx-glr-download
:download:`Download Python source code: plot_gromov_barycenter.py <plot_gromov_barycenter.py>`
.. container:: sphx-glr-download
:download:`Download Jupyter notebook: plot_gromov_barycenter.ipynb <plot_gromov_barycenter.ipynb>`
.. only:: html
.. rst-class:: sphx-glr-signature
`Gallery generated by Sphinx-Gallery <https://sphinx-gallery.readthedocs.io>`_
|
