update doc

pina/problem/abstract_problem.py

@@ -47,7 +47,7 @@ class AbstractProblem(metaclass=ABCMeta):
         Get batching dimension.
 
         :return: The batching dimension.
-        :rtype int
+        :rtype: int
         """
         return self._batching_dimension
 
@@ -85,7 +85,7 @@ class AbstractProblem(metaclass=ABCMeta):
         points.
 
         :return: The discretised domains.
-        :rtype dict
+        :rtype: dict
         """
         return self._discretised_domains
 
@@ -178,13 +178,28 @@ class AbstractProblem(metaclass=ABCMeta):
             chebyshev sampling, ``chebyshev``; grid sampling ``grid``.
         :param domains: The domains from which to sample. Default is ``all``.
         :type domains: str | list[str]
-        :param dict sample_rules: A dictionary of custom sampling rules.
+        :param dict sample_rules: A dictionary defining custom sampling rules 
+            for input variables. If provided, it must contain a dictionary 
+            specifying the sampling rule for each variable, overriding the 
+            ``n`` and ``mode`` arguments. Each key must correspond to the 
+            input variables from 
+            :meth:~pina.problem.AbstractProblem.input_variables, and its value 
+            should be another dictionary with 
+            two keys: ``n`` (number of points to sample) and ``mode`` 
+            (sampling method). Defaults to None.
         :raises RuntimeError: If both ``n`` and ``sample_rules`` are specified.
         :raises RuntimeError: If neither ``n`` nor ``sample_rules`` are set.
 
         :Example:
             >>> problem.discretise_domain(n=10, mode='grid')
             >>> problem.discretise_domain(n=10, mode='grid', domains=['gamma1'])
+            >>> problem.discretise_domain(
+            ...     sample_rules={
+            ...         'x': {'n': 10, 'mode': 'grid'},
+            ...         'y': {'n': 100, 'mode': 'grid'}
+            ...     },
+            ...     domains=['D']
+            ... )
 
         .. warning::
             ``random`` is currently the only implemented ``mode`` for all
@@ -197,6 +212,11 @@ class AbstractProblem(metaclass=ABCMeta):
             :class:`~pina.domain.intersection_domain.Intersection`.
             The modes ``latin`` or ``lh``,  ``chebyshev``, ``grid`` are only
             implemented for :class:`~pina.domain.cartesian.CartesianDomain`.
+
+        .. warning::
+            If custom discretisation is applied by setting ``sample_rules`` not 
+            to ``None``, then the discretised domain must be of class 
+            :class:`~pina.domain.cartesian.CartesianDomain`
         """
 
         # check consistecy n, mode, variables, locations