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diff --git a/examples/gromov/plot_gromov_wasserstein_dictionary_learning.py b/examples/gromov/plot_gromov_wasserstein_dictionary_learning.py
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+# -*- coding: utf-8 -*-
+
+r"""
+=================================
+(Fused) Gromov-Wasserstein Linear Dictionary Learning
+=================================
+
+In this exemple, we illustrate how to learn a Gromov-Wasserstein dictionary on
+a dataset of structured data such as graphs, denoted
+:math:`\{ \mathbf{C_s} \}_{s \in [S]}` where every nodes have uniform weights.
+Given a dictionary :math:`\mathbf{C_{dict}}` composed of D structures of a fixed
+size nt, each graph :math:`(\mathbf{C_s}, \mathbf{p_s})`
+is modeled as a convex combination :math:`\mathbf{w_s} \in \Sigma_D` of these
+dictionary atoms as :math:`\sum_d w_{s,d} \mathbf{C_{dict}[d]}`.
+
+
+First, we consider a dataset composed of graphs generated by Stochastic Block models
+with variable sizes taken in :math:`\{30, ... , 50\}` and quantities of clusters
+varying in :math:`\{ 1, 2, 3\}`. We learn a dictionary of 3 atoms, by minimizing
+the Gromov-Wasserstein distance from all samples to its model in the dictionary
+with respect to the dictionary atoms.
+
+Second, we illustrate the extension of this dictionary learning framework to
+structured data endowed with node features by using the Fused Gromov-Wasserstein
+distance. Starting from the aforementioned dataset of unattributed graphs, we
+add discrete labels uniformly depending on the number of clusters. Then we learn
+and visualize attributed graph atoms where each sample is modeled as a joint convex
+combination between atom structures and features.
+
+
+[38] C. Vincent-Cuaz, T. Vayer, R. Flamary, M. Corneli, N. Courty, Online Graph
+Dictionary Learning, International Conference on Machine Learning (ICML), 2021.
+
+"""
+# Author: Cédric Vincent-Cuaz <cedric.vincent-cuaz@inria.fr>
+#
+# License: MIT License
+
+# sphinx_gallery_thumbnail_number = 4
+
+import numpy as np
+import matplotlib.pylab as pl
+from sklearn.manifold import MDS
+from ot.gromov import gromov_wasserstein_linear_unmixing, gromov_wasserstein_dictionary_learning, fused_gromov_wasserstein_linear_unmixing, fused_gromov_wasserstein_dictionary_learning
+import ot
+import networkx
+from networkx.generators.community import stochastic_block_model as sbm
+# %%
+# =============================================================================
+# Generate a dataset composed of graphs following Stochastic Block models of 1, 2 and 3 clusters.
+# =============================================================================
+
+np.random.seed(42)
+
+N = 60  # number of graphs in the dataset
+# For every number of clusters, we generate SBM with fixed inter/intra-clusters probability.
+clusters = [1, 2, 3]
+Nc = N // len(clusters)  # number of graphs by cluster
+nlabels = len(clusters)
+dataset = []
+labels = []
+
+p_inter = 0.1
+p_intra = 0.9
+for n_cluster in clusters:
+    for i in range(Nc):
+        n_nodes = int(np.random.uniform(low=30, high=50))
+
+        if n_cluster > 1:
+            P = p_inter * np.ones((n_cluster, n_cluster))
+            np.fill_diagonal(P, p_intra)
+        else:
+            P = p_intra * np.eye(1)
+        sizes = np.round(n_nodes * np.ones(n_cluster) / n_cluster).astype(np.int32)
+        G = sbm(sizes, P, seed=i, directed=False)
+        C = networkx.to_numpy_array(G)
+        dataset.append(C)
+        labels.append(n_cluster)
+
+
+# Visualize samples
+
+def plot_graph(x, C, binary=True, color='C0', s=None):
+    for j in range(C.shape[0]):
+        for i in range(j):
+            if binary:
+                if C[i, j] > 0:
+                    pl.plot([x[i, 0], x[j, 0]], [x[i, 1], x[j, 1]], alpha=0.2, color='k')
+            else:  # connection intensity proportional to C[i,j]
+                pl.plot([x[i, 0], x[j, 0]], [x[i, 1], x[j, 1]], alpha=C[i, j], color='k')
+
+    pl.scatter(x[:, 0], x[:, 1], c=color, s=s, zorder=10, edgecolors='k', cmap='tab10', vmax=9)
+
+
+pl.figure(1, (12, 8))
+pl.clf()
+for idx_c, c in enumerate(clusters):
+    C = dataset[(c - 1) * Nc]  # sample with c clusters
+    # get 2d position for nodes
+    x = MDS(dissimilarity='precomputed', random_state=0).fit_transform(1 - C)
+    pl.subplot(2, nlabels, c)
+    pl.title('(graph) sample from label ' + str(c), fontsize=14)
+    plot_graph(x, C, binary=True, color='C0', s=50.)
+    pl.axis("off")
+    pl.subplot(2, nlabels, nlabels + c)
+    pl.title('(matrix) sample from label %s \n' % c, fontsize=14)
+    pl.imshow(C, interpolation='nearest')
+    pl.axis("off")
+pl.tight_layout()
+pl.show()
+
+# %%
+# =============================================================================
+# Estimate the gromov-wasserstein dictionary from the dataset
+# =============================================================================
+
+
+np.random.seed(0)
+ps = [ot.unif(C.shape[0]) for C in dataset]
+
+D = 3  # 3 atoms in the dictionary
+nt = 6  # of 6 nodes each
+
+q = ot.unif(nt)
+reg = 0.  # regularization coefficient to promote sparsity of unmixings {w_s}
+
+Cdict_GW, log = gromov_wasserstein_dictionary_learning(
+    Cs=dataset, D=D, nt=nt, ps=ps, q=q, epochs=10, batch_size=16,
+    learning_rate=0.1, reg=reg, projection='nonnegative_symmetric',
+    tol_outer=10**(-5), tol_inner=10**(-5), max_iter_outer=30, max_iter_inner=300,
+    use_log=True, use_adam_optimizer=True, verbose=True
+)
+# visualize loss evolution over epochs
+pl.figure(2, (4, 3))
+pl.clf()
+pl.title('loss evolution by epoch', fontsize=14)
+pl.plot(log['loss_epochs'])
+pl.xlabel('epochs', fontsize=12)
+pl.ylabel('loss', fontsize=12)
+pl.tight_layout()
+pl.show()
+
+# %%
+# =============================================================================
+# Visualization of the estimated dictionary atoms
+# =============================================================================
+
+
+# Continuous connections between nodes of the atoms are colored in shades of grey (1: dark / 2: white)
+
+pl.figure(3, (12, 8))
+pl.clf()
+for idx_atom, atom in enumerate(Cdict_GW):
+    scaled_atom = (atom - atom.min()) / (atom.max() - atom.min())
+    x = MDS(dissimilarity='precomputed', random_state=0).fit_transform(1 - scaled_atom)
+    pl.subplot(2, D, idx_atom + 1)
+    pl.title('(graph) atom ' + str(idx_atom + 1), fontsize=14)
+    plot_graph(x, atom / atom.max(), binary=False, color='C0', s=100.)
+    pl.axis("off")
+    pl.subplot(2, D, D + idx_atom + 1)
+    pl.title('(matrix) atom %s \n' % (idx_atom + 1), fontsize=14)
+    pl.imshow(scaled_atom, interpolation='nearest')
+    pl.colorbar()
+    pl.axis("off")
+pl.tight_layout()
+pl.show()
+#%%
+# =============================================================================
+# Visualization of the embedding space
+# =============================================================================
+
+unmixings = []
+reconstruction_errors = []
+for C in dataset:
+    p = ot.unif(C.shape[0])
+    unmixing, Cembedded, OT, reconstruction_error = gromov_wasserstein_linear_unmixing(
+        C, Cdict_GW, p=p, q=q, reg=reg,
+        tol_outer=10**(-5), tol_inner=10**(-5),
+        max_iter_outer=30, max_iter_inner=300
+    )
+    unmixings.append(unmixing)
+    reconstruction_errors.append(reconstruction_error)
+unmixings = np.array(unmixings)
+print('cumulated reconstruction error:', np.array(reconstruction_errors).sum())
+
+
+# Compute the 2D representation of the unmixing living in the 2-simplex of probability
+unmixings2D = np.zeros(shape=(N, 2))
+for i, w in enumerate(unmixings):
+    unmixings2D[i, 0] = (2. * w[1] + w[2]) / 2.
+    unmixings2D[i, 1] = (np.sqrt(3.) * w[2]) / 2.
+x = [0., 0.]
+y = [1., 0.]
+z = [0.5, np.sqrt(3) / 2.]
+extremities = np.stack([x, y, z])
+
+pl.figure(4, (4, 4))
+pl.clf()
+pl.title('Embedding space', fontsize=14)
+for cluster in range(nlabels):
+    start, end = Nc * cluster, Nc * (cluster + 1)
+    if cluster == 0:
+        pl.scatter(unmixings2D[start:end, 0], unmixings2D[start:end, 1], c='C' + str(cluster), marker='o', s=40., label='1 cluster')
+    else:
+        pl.scatter(unmixings2D[start:end, 0], unmixings2D[start:end, 1], c='C' + str(cluster), marker='o', s=40., label='%s clusters' % (cluster + 1))
+pl.scatter(extremities[:, 0], extremities[:, 1], c='black', marker='x', s=80., label='atoms')
+pl.plot([x[0], y[0]], [x[1], y[1]], color='black', linewidth=2.)
+pl.plot([x[0], z[0]], [x[1], z[1]], color='black', linewidth=2.)
+pl.plot([y[0], z[0]], [y[1], z[1]], color='black', linewidth=2.)
+pl.axis('off')
+pl.legend(fontsize=11)
+pl.tight_layout()
+pl.show()
+# %%
+# =============================================================================
+# Endow the dataset with node features
+# =============================================================================
+
+# We follow this feature assignment on all nodes of a graph depending on its label/number of clusters
+# 1 cluster --> 0 as nodes feature
+# 2 clusters --> 1 as nodes feature
+# 3 clusters --> 2 as nodes feature
+# features are one-hot encoded following these assignments
+dataset_features = []
+for i in range(len(dataset)):
+    n = dataset[i].shape[0]
+    F = np.zeros((n, 3))
+    if i < Nc:  # graph with 1 cluster
+        F[:, 0] = 1.
+    elif i < 2 * Nc:  # graph with 2 clusters
+        F[:, 1] = 1.
+    else:  # graph with 3 clusters
+        F[:, 2] = 1.
+    dataset_features.append(F)
+
+pl.figure(5, (12, 8))
+pl.clf()
+for idx_c, c in enumerate(clusters):
+    C = dataset[(c - 1) * Nc]  # sample with c clusters
+    F = dataset_features[(c - 1) * Nc]
+    colors = ['C' + str(np.argmax(F[i])) for i in range(F.shape[0])]
+    # get 2d position for nodes
+    x = MDS(dissimilarity='precomputed', random_state=0).fit_transform(1 - C)
+    pl.subplot(2, nlabels, c)
+    pl.title('(graph) sample from label ' + str(c), fontsize=14)
+    plot_graph(x, C, binary=True, color=colors, s=50)
+    pl.axis("off")
+    pl.subplot(2, nlabels, nlabels + c)
+    pl.title('(matrix) sample from label %s \n' % c, fontsize=14)
+    pl.imshow(C, interpolation='nearest')
+    pl.axis("off")
+pl.tight_layout()
+pl.show()
+# %%
+# =============================================================================
+# Estimate a Fused Gromov-Wasserstein dictionary from the dataset of attributed graphs
+# =============================================================================
+np.random.seed(0)
+ps = [ot.unif(C.shape[0]) for C in dataset]
+D = 3  # 6 atoms instead of 3
+nt = 6
+q = ot.unif(nt)
+reg = 0.001
+alpha = 0.5  # trade-off parameter between structure and feature information of Fused Gromov-Wasserstein
+
+
+Cdict_FGW, Ydict_FGW, log = fused_gromov_wasserstein_dictionary_learning(
+    Cs=dataset, Ys=dataset_features, D=D, nt=nt, ps=ps, q=q, alpha=alpha,
+    epochs=10, batch_size=16, learning_rate_C=0.1, learning_rate_Y=0.1, reg=reg,
+    tol_outer=10**(-5), tol_inner=10**(-5), max_iter_outer=30, max_iter_inner=300,
+    projection='nonnegative_symmetric', use_log=True, use_adam_optimizer=True, verbose=True
+)
+# visualize loss evolution
+pl.figure(6, (4, 3))
+pl.clf()
+pl.title('loss evolution by epoch', fontsize=14)
+pl.plot(log['loss_epochs'])
+pl.xlabel('epochs', fontsize=12)
+pl.ylabel('loss', fontsize=12)
+pl.tight_layout()
+pl.show()
+
+# %%
+# =============================================================================
+# Visualization of the estimated dictionary atoms
+# =============================================================================
+
+pl.figure(7, (12, 8))
+pl.clf()
+max_features = Ydict_FGW.max()
+min_features = Ydict_FGW.min()
+
+for idx_atom, (Catom, Fatom) in enumerate(zip(Cdict_FGW, Ydict_FGW)):
+    scaled_atom = (Catom - Catom.min()) / (Catom.max() - Catom.min())
+    #scaled_F = 2 * (Fatom - min_features) / (max_features - min_features)
+    colors = ['C%s' % np.argmax(Fatom[i]) for i in range(Fatom.shape[0])]
+    x = MDS(dissimilarity='precomputed', random_state=0).fit_transform(1 - scaled_atom)
+    pl.subplot(2, D, idx_atom + 1)
+    pl.title('(attributed graph) atom ' + str(idx_atom + 1), fontsize=14)
+    plot_graph(x, Catom / Catom.max(), binary=False, color=colors, s=100)
+    pl.axis("off")
+    pl.subplot(2, D, D + idx_atom + 1)
+    pl.title('(matrix) atom %s \n' % (idx_atom + 1), fontsize=14)
+    pl.imshow(scaled_atom, interpolation='nearest')
+    pl.colorbar()
+    pl.axis("off")
+pl.tight_layout()
+pl.show()
+
+# %%
+# =============================================================================
+# Visualization of the embedding space
+# =============================================================================
+
+unmixings = []
+reconstruction_errors = []
+for i in range(len(dataset)):
+    C = dataset[i]
+    Y = dataset_features[i]
+    p = ot.unif(C.shape[0])
+    unmixing, Cembedded, Yembedded, OT, reconstruction_error = fused_gromov_wasserstein_linear_unmixing(
+        C, Y, Cdict_FGW, Ydict_FGW, p=p, q=q, alpha=alpha,
+        reg=reg, tol_outer=10**(-6), tol_inner=10**(-6), max_iter_outer=30, max_iter_inner=300
+    )
+    unmixings.append(unmixing)
+    reconstruction_errors.append(reconstruction_error)
+unmixings = np.array(unmixings)
+print('cumulated reconstruction error:', np.array(reconstruction_errors).sum())
+
+# Visualize unmixings in the 2-simplex of probability
+unmixings2D = np.zeros(shape=(N, 2))
+for i, w in enumerate(unmixings):
+    unmixings2D[i, 0] = (2. * w[1] + w[2]) / 2.
+    unmixings2D[i, 1] = (np.sqrt(3.) * w[2]) / 2.
+x = [0., 0.]
+y = [1., 0.]
+z = [0.5, np.sqrt(3) / 2.]
+extremities = np.stack([x, y, z])
+
+pl.figure(8, (4, 4))
+pl.clf()
+pl.title('Embedding space', fontsize=14)
+for cluster in range(nlabels):
+    start, end = Nc * cluster, Nc * (cluster + 1)
+    if cluster == 0:
+        pl.scatter(unmixings2D[start:end, 0], unmixings2D[start:end, 1], c='C' + str(cluster), marker='o', s=40., label='1 cluster')
+    else:
+        pl.scatter(unmixings2D[start:end, 0], unmixings2D[start:end, 1], c='C' + str(cluster), marker='o', s=40., label='%s clusters' % (cluster + 1))
+
+pl.scatter(extremities[:, 0], extremities[:, 1], c='black', marker='x', s=80., label='atoms')
+pl.plot([x[0], y[0]], [x[1], y[1]], color='black', linewidth=2.)
+pl.plot([x[0], z[0]], [x[1], z[1]], color='black', linewidth=2.)
+pl.plot([y[0], z[0]], [y[1], z[1]], color='black', linewidth=2.)
+pl.axis('off')
+pl.legend(fontsize=11)
+pl.tight_layout()
+pl.show()