Revert PyTorch NNCG optimizer doc build; Try torch v2 for Sphinx

deepxde/optimizers/__init__.py

@@ -1,22 +1,10 @@
 import importlib
-import os
 import sys
 
 from .config import LBFGS_options, set_LBFGS_options, NNCG_options, set_NNCG_options
 from ..backend import backend_name
 
 
-# To get Sphinx documentation to build, we import all
-if os.environ.get("READTHEDOCS") == "True":
-    # The backend should be tensorflow/tensorflow.compat.v1 to ensure backend.tf is not
-    # None.
-    from . import jax
-    from . import paddle
-    from . import pytorch
-    from . import tensorflow
-    from . import tensorflow_compat_v1
-
-
 def _load_backend(mod_name):
     mod = importlib.import_module(".%s" % mod_name, __name__)
     thismod = sys.modules[__name__]

deepxde/optimizers/pytorch/__init__.py

@@ -1,4 +1,3 @@
 __all__ = ["get", "is_external_optimizer"]
 
-from .nncg import NNCG  # To get Sphinx documentation to build
 from .optimizers import get, is_external_optimizer

docs/requirements.txt

@@ -9,7 +9,7 @@ tensorflow>=2.7.0
 # TensorFlow 2.x
 tensorflow-probability>=0.11.0
 # PyTorch
-torch<2.0.0  # build fails on RTD with torch 2.0.0
+torch
 # PaddlePaddle
 # https://paddle-wheel.bj.bcebos.com/develop/linux/linux-cpu-mkl-avx/paddlepaddle-0.0.0-cp38-cp38-linux_x86_64.whl
 paddlepaddle==2.6.0