Add SINDy model (#660)

pina/model/__init__.py

@@ -15,6 +15,7 @@ __all__ = [
     "GraphNeuralOperator",
     "PirateNet",
     "EquivariantGraphNeuralOperator",
+    "SINDy",
 ]
 
 from .feed_forward import FeedForward, ResidualFeedForward
@@ -28,3 +29,4 @@ from .spline import Spline
 from .graph_neural_operator import GraphNeuralOperator
 from .pirate_network import PirateNet
 from .equivariant_graph_neural_operator import EquivariantGraphNeuralOperator
+from .sindy import SINDy