Add intersphinx

docs/source/conf.py

@@ -3,12 +3,19 @@ import nifty8
 needs_sphinx = '3.2.0'
 
 extensions = [
-    'sphinx.ext.napoleon',  # Support for NumPy and Google style docstrings
-    'sphinx.ext.imgmath',  # Render math as images
-    'sphinx.ext.viewcode'  # Add links to highlighted source code
+    'sphinx.ext.napoleon',   # Support for NumPy and Google style docstrings
+    'sphinx.ext.imgmath',    # Render math as images
+    'sphinx.ext.viewcode',   # Add links to highlighted source code
+    'sphinx.ext.intersphinx' # Links to other sphinx docs (mostly numpy)
 ]
 master_doc = 'index'
 
+intersphinx_mapping = {"numpy": ("https://numpy.org/doc/stable/", None),
+                       #"matplotlib": ('https://matplotlib.org/stable/', None),
+                       "ducc0": ("https://mtr.pages.mpcdf.de/ducc/", None),
+                       "scipy": ('https://docs.scipy.org/doc/scipy/reference/', None),
+                       }
+
 napoleon_google_docstring = False
 napoleon_numpy_docstring = True
 napoleon_use_ivar = True

src/operators/matrix_product_operator.py

@@ -16,6 +16,7 @@
 # NIFTy is being developed at the Max-Planck-Institut fuer Astrophysik.
 
 import numpy as np
+import scipy.sparse
 
 from .. import utilities
 from ..domain_tuple import DomainTuple
@@ -45,10 +46,10 @@ class MatrixProductOperator(EndomorphicOperator):
 
     Parameters
     ----------
-    domain: :class:`Domain` or :class:`DomainTuple`
+    domain: Domain or DomainTuple
         Domain of the operator.
         If :class:`DomainTuple` it is assumed to have only one entry.
-    matrix: scipy.sparse matrix or numpy array
+    matrix: scipy.sparse.spmatrix or numpy.ndarray
         Quadratic matrix of shape `(domain.shape, domain.shape)`
         (if `not flatten`) that supports `matrix.transpose()`.
         If it is not a numpy array, needs to be applicable to the val