Docs (#81)

* clean `condition` module
* add docs

pina/problem/timedep_problem.py

@@ -16,29 +16,29 @@ class TimeDependentProblem(AbstractProblem):
         >>> from pina.operators import grad, nabla
         >>> from pina import Condition, Span
         >>> import torch
-
+        >>>
         >>> class Wave(TimeDependentSpatialProblem):
-
+        >>>
         >>>     output_variables = ['u']
         >>>     spatial_domain = Span({'x': [0, 3]})
         >>>     temporal_domain = Span({'t': [0, 1]})
-
+        >>>
         >>>     def wave_equation(input_, output_):
         >>>         u_t = grad(output_, input_, components=['u'], d=['t'])
         >>>         u_tt = grad(u_t, input_, components=['dudt'], d=['t'])
         >>>         nabla_u = nabla(output_, input_, components=['u'], d=['x'])
         >>>         return nabla_u - u_tt
-
+        >>>
         >>>     def nil_dirichlet(input_, output_):
         >>>         value = 0.0
         >>>         return output_.extract(['u']) - value
-
+        >>>
         >>>     def initial_condition(input_, output_):
         >>>         u_expected = (-3*torch.sin(2*torch.pi*input_.extract(['x']))
         >>>             + 5*torch.sin(8/3*torch.pi*input_.extract(['x'])))
         >>>         u = output_.extract(['u'])
         >>>         return u - u_expected
-
+        >>>
         >>>     conditions = {
         >>>         't0': Condition(Span({'x': [0, 3], 't':0}), initial_condition),
         >>>         'gamma1': Condition(Span({'x':0, 't':[0, 1]}), nil_dirichlet),