fix grad sign

Author: cedricvincentcuaz

ot/gromov/_semirelaxed.py

@@ -250,7 +250,7 @@ def semirelaxed_gromov_wasserstein2(C1, C2, p=None, loss_fun='square_loss', symm
 
     elif loss_fun == 'kl_loss':
         gC1 = nx.log(C1 + 1e-15) * nx.outer(p, p) - nx.dot(T, nx.dot(nx.log(C2 + 1e-15), T.T))
-        gC2 = nx.dot(T.T, nx.dot(C1, T)) / (C2 + 1e-15) + nx.outer(q, q)
+        gC2 = - nx.dot(T.T, nx.dot(C1, T)) / (C2 + 1e-15) + nx.outer(q, q)
 
     srgw = nx.set_gradients(srgw, (C1, C2), (gC1, gC2))
 
@@ -509,7 +509,7 @@ def semirelaxed_fused_gromov_wasserstein2(M, C1, C2, p=None, loss_fun='square_lo
 
     elif loss_fun == 'kl_loss':
         gC1 = nx.log(C1 + 1e-15) * nx.outer(p, p) - nx.dot(T, nx.dot(nx.log(C2 + 1e-15), T.T))
-        gC2 = nx.dot(T.T, nx.dot(C1, T)) / (C2 + 1e-15) + nx.outer(q, q)
+        gC2 = - nx.dot(T.T, nx.dot(C1, T)) / (C2 + 1e-15) + nx.outer(q, q)
 
     if isinstance(alpha, int) or isinstance(alpha, float):
         srfgw_dist = nx.set_gradients(srfgw_dist, (C1, C2, M),