fix rendering part 2

pina/problem/zoo/advection.py

@@ -63,6 +63,9 @@ class AdvectionProblem(SpatialProblem, TimeDependentProblem):
         training physics-informed neural networks*.
         arXiv preprint arXiv:2308.08468 (2023).
         DOI: `arXiv:2308.08468  <https://arxiv.org/abs/2308.08468>`_.
+
+    :Example:
+        >>> problem = AdvectionProblem(c=1.0)
     """
 
     output_variables = ["u"]

pina/problem/zoo/allen_cahn.py

@@ -49,6 +49,9 @@ class AllenCahnProblem(TimeDependentProblem, SpatialProblem):
         Computer Methods in Applied Mechanics and Engineering 421 (2024): 116805
         DOI: `10.1016/
         j.cma.2024.116805 <https://doi.org/10.1016/j.cma.2024.116805>`_.
+    
+    :Example:
+        >>> problem = AllenCahnProblem()
     """
 
     output_variables = ["u"]

pina/problem/zoo/diffusion_reaction.py

@@ -59,6 +59,9 @@ class DiffusionReactionProblem(TimeDependentProblem, SpatialProblem):
         **Original reference**: Si, Chenhao, et al. *Complex Physics-Informed
         Neural Network.* arXiv preprint arXiv:2502.04917 (2025).
         DOI: `arXiv:2502.04917 <https://arxiv.org/abs/2502.04917>`_.
+
+    :Example:
+        >>> problem = DiffusionReactionProblem()
     """
 
     output_variables = ["u"]

pina/problem/zoo/helmholtz.py

@@ -53,6 +53,9 @@ class HelmholtzProblem(SpatialProblem):
         **Original reference**: Si, Chenhao, et al. *Complex Physics-Informed
         Neural Network.* arXiv preprint arXiv:2502.04917 (2025).
         DOI: `arXiv:2502.04917 <https://arxiv.org/abs/2502.04917>`_.
+    
+    :Example:
+        >>> problem = HelmholtzProblem()
     """
 
     output_variables = ["u"]

pina/problem/zoo/inverse_poisson_2d_square.py

@@ -50,6 +50,9 @@ class InversePoisson2DSquareProblem(SpatialProblem, InverseProblem):
     Implementation of the inverse 2-dimensional Poisson problem in the square
     domain :math:`[0, 1] \times [0, 1]`,
     with unknown parameter domain :math:`[-1, 1] \times [-1, 1]`.
+
+    :Example:
+        >>> problem = InversePoisson2DSquareProblem()
     """
 
     output_variables = ["u"]

pina/problem/zoo/poisson_2d_square.py

@@ -30,6 +30,9 @@ class Poisson2DSquareProblem(SpatialProblem):
     r"""
     Implementation of the 2-dimensional Poisson problem in the square domain
     :math:`[0, 1] \times [0, 1]`.
+
+    :Example:
+        >>> problem = Poisson2DSquareProblem()
     """
 
     output_variables = ["u"]