%matplotlib inline
This example is designed to show how to use the Gromov-Wasserstein distance computation in POT.
# 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
This function allows to find an embedding of points given a dissimilarity matrix that will be given by the output of the algorithm
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
The four distributions are constructed from 4 simple images
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])])
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)
The PCA helps in getting consistency between the rotations
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')
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