Add plot in tutorials 1,3,4,9

tutorials/tutorial1/tutorial.ipynb

@@ -137,15 +137,7 @@
    "execution_count": 2,
    "id": "f2608e2e",
    "metadata": {},
-   "outputs": [
-    {
-     "name": "stderr",
-     "output_type": "stream",
-     "text": [
-      "/home/matte_b/PINA/pina/operators.py: DeprecationWarning: 'pina.operators' is deprecated and will be removed in future versions. Please use 'pina.operator' instead.\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
     "from pina.problem import SpatialProblem\n",
     "from pina.operator import grad\n",

tutorials/tutorial1/tutorial.py

@@ -89,7 +89,7 @@ class TimeSpaceODE(SpatialProblem, TimeDependentProblem):
 # 
 # Once the `Problem` class is initialized, we need to represent the differential equation in **PINA**. In order to do this, we need to load the **PINA** operators from `pina.operators` module. Again, we'll consider Equation (1) and represent it in **PINA**:
 
-# In[ ]:
+# In[2]:
 
 
 from pina.problem import SpatialProblem