Update solvers (#434)

* Enable DDP training with batch_size=None and add validity check for split sizes
* Refactoring SolverInterfaces (#435)
* Solver update + weighting
* Updating PINN for 0.2
* Modify GAROM + tests
* Adding more versatile loggers
* Disable compilation when running on Windows
* Fix tests

---------

Co-authored-by: giovanni <giovanni.canali98@yahoo.it>
Co-authored-by: FilippoOlivo <filippo@filippoolivo.com>

pina/optim/torch_optimizer.py

@@ -13,11 +13,14 @@ class TorchOptimizer(Optimizer):
 
         self.optimizer_class = optimizer_class
         self.kwargs = kwargs
-        self.optimizer_instance = None
+        self._optimizer_instance = None
 
     def hook(self, parameters):
-        self.optimizer_instance = self.optimizer_class(parameters,
+        self._optimizer_instance = self.optimizer_class(parameters,
                                                        **self.kwargs)
     @property
     def instance(self):
-        return self.optimizer_instance
+        """
+        Optimizer instance.
+        """
+        return self._optimizer_instance