diff --git a/hysop/core/graph/computational_node_frontend.py b/hysop/core/graph/computational_node_frontend.py
index 5ba94835576d20bbc1f330bc6befd05377210a3e..2066a2247eb1d1f218076cfdfa6039125922dbee 100644
--- a/hysop/core/graph/computational_node_frontend.py
+++ b/hysop/core/graph/computational_node_frontend.py
@@ -157,13 +157,13 @@ class ComputationalGraphNodeFrontend(ComputationalGraphNodeGenerator):
         try:
             op = self.impl(**self.impl_kwds)
         except:
-            sargs = [f"*{k} = {v.__class__}" for (k, v) in self.impl_kwds.items()]
-            msg = "FATAL ERROR during {}.generate():\n"
-            msg += " => failed to initialize an instance of type {}"
-            msg += "\n    by using the following keyword arguments:"
-            msg += "\n     " + "\n     ".join(sargs)
-            msg = msg.format(self.__class__, self.impl)
-            print(f"\n{msg}")
+            sargs = [f'*{k} = {repr(v)}'
+                     for (k, v) in self.impl_kwds.items()]
+            msg = f'FATAL ERROR during {self.__class__}.generate():\n'
+            msg += f' => failed to initialize an instance of type {self.impl}'
+            msg += '\n    by using the following keyword arguments:'
+            msg += '\n     '+'\n     '.join(sargs)
+            print(f'\n{msg}')
             raise
 
         for kwds in self._input_fields_to_dump:
diff --git a/hysop/numerics/stencil/stencil_generator.py b/hysop/numerics/stencil/stencil_generator.py
index 92e475655026b7b0756838b30c9d391d6adb15b3..caa47f0d80d1d9f39c0fd3ef6ad18a267c07188e 100644
--- a/hysop/numerics/stencil/stencil_generator.py
+++ b/hysop/numerics/stencil/stencil_generator.py
@@ -666,15 +666,13 @@ if __name__ == "__main__":
             print(f"  origin: {i} =>  {stencil.factor} . {stencil.coeffs}")
 
         sg.configure(dim=1, derivative=1, order=2, dtype=np.float64)
-        print(
-            "\ndim=1, 1st order first derivative, np.float64, approximative, shape=(5,):"
-        )
+        print('\ndim=1, 1st order first derivative, np.float64, approximative, shape=(5,):')
         for i in range(sg.get_config().shape()[0]):
             stencil = sg.generate_approximative_stencil(origin=i).reshape((5,))
             print(f"  origin: {i} =>  {stencil.factor} . {stencil.coeffs}")
 
         sg.configure(dim=1, derivative=2, order=2, dtype=np.float64)
-        print("\ndim=1, 2nd order first derivative, np.float64, approximative:")
+        print('\ndim=1, 2nd order first derivative, np.float64, approximative:')
         for i in range(sg.get_config().shape()[0]):
             stencil = sg.generate_approximative_stencil(origin=i)
             print(f"  origin: {i} =>  {stencil.factor} . {stencil.coeffs}")
@@ -710,13 +708,13 @@ if __name__ == "__main__":
         sg.configure(derivative=2)
         print("\nCentered second order derivative stencils:")
         for i in range(1, 4):
-            stencil = sg.generate_approximative_stencil(order=2 * i, dtype=np.float16)
-            print(f"  {stencil.coeffs}")
+            stencil = sg.generate_approximative_stencil(order=2*i, dtype=np.float16)
+            print(f'  {stencil.coeffs}')
         print()
         for i in range(1, 4):
             stencil = sg.generate_approximative_stencil(order=2 * i, dtype=MPQ)
             print(f"  {stencil.coeffs}")
         print()
         for i in range(1, 4):
-            stencil = sg.generate_exact_stencil(order=2 * i)
-            print(f"  {stencil.coeffs}")
+            stencil = sg.generate_exact_stencil(order=2*i)
+            print(f'  {stencil.coeffs}')
diff --git a/hysop/simulation.py b/hysop/simulation.py
index 38d889038df13f86f705043719e5eb3d4095552c..ced67e6dd00f6aceaa0e9e78567d01fcafddf85a 100644
--- a/hysop/simulation.py
+++ b/hysop/simulation.py
@@ -176,8 +176,8 @@ class Simulation:
         else:
             raise ValueError("You must set nb_iter or dt0 value.")
 
-        msg = f"dt0={dt0}, start={start}, end={end}"
-        assert (dt0 > 0.0) and (dt0 <= (end - start)), msg
+        msg = f'dt0={dt0}, start={start}, end={end}'
+        assert (dt0 > 0.0) and -1e-6 < ((end-start)-dt0)/dt0, msg
         self._dt0 = dt0
 
         dt_name = f"{name}_dt" if (name is not None) else "dt"