update doc

ot/solvers.py

@@ -130,7 +130,7 @@ def solve(
         outputs (`plan, value, value_linear`) but with important memory cost.
         'envelope' provides gradients only for `value` and and other outputs are
         detached. This is useful for memory saving when only the value is needed. 'last_step' provides
-        gradients only for the last iteration of the Sinkhorn solver.
+        gradients only for the last iteration of the Sinkhorn solver, but provides gradient for both the OT plan and the objective values.
 
     Returns
     -------
@@ -412,9 +412,10 @@ def solve(
                 potentials = (log["u"], log["v"])
 
             elif reg_type.lower() in ["entropy", "kl"]:
-                if (
-                    grad in ["envelope",  "last_step"]
-                ):  # if envelope or last_step then detach the input
+                if grad in [
+                    "envelope",
+                    "last_step",
+                ]:  # if envelope or last_step then detach the input
                     M0, a0, b0 = M, a, b
                     M, a, b = nx.detach(M, a, b)