work on docs

docs/source/concepts/domains.rst

-Domains
-=======
+NIFTy's domain classes
+======================
 
-Description of Domains
+.. currentmodule:: nifty4
+
+
+**Abstract base class**
+
+:py:class:`Domain` is the abstract ancestor for all of NIFTy's domains.
 
 .. toctree::
     :maxdepth: 1
-    :caption: Types of Domains
-
-    DOF                             <../mod/nifty4.domains.dof_space>
-    Gauss-Legendre                  <../mod/nifty4.domains.gl_space>
-    HEALPix                         <../mod/nifty4.domains.hp_space>
-    Power                           <../mod/nifty4.domains.power_space>
-    LM                              <../mod/nifty4.domains.lm_space>
-    RG                              <../mod/nifty4.domains.rg_space>
+
     Domain                          <../mod/nifty4.domains.domain>
-    Structured Domain               <../mod/nifty4.domains.structured_domain>
-    Unstructured Domain             <../mod/nifty4.domains.unstructured_domain>
+
+
+**Unstructured domains**
+
+Domains can be either *structured* (i.e. there is geometrical information
+associated with them, like position in space and volume factors),
+or *unstructured* (meaning that the data points have no associated manifold).
+
+Unstructured domains can be described by instances of NIFTy's
+:py:class:`UnstructuredDomain` class.
+
+.. toctree::
+    :maxdepth: 1
+
+    UnstructuredDomain              <../mod/nifty4.domains.unstructured_domain>
+
+
+**Structured domains**
+
+In contrast to unstructured domains, these domains have an assigned geometry.
+NIFTy requires these domains to provide the volume elements of their grid cells.
+The additional methods are described in the abstract class
+:py:class:`StructuredDomain`.
+
+.. toctree::
+    :maxdepth: 1
+
+    StructuredDomain                <../mod/nifty4.domains.structured_domain>
+
+NIFTy comes with several concrete subclasses of :py:class:`StructuredDomain`.
+
+:py:class:`RGSpace` represents a regular Cartesian grid with an arbitrary
+number of dimensions, which is supposed to be periodic in each dimension.
+This domain can be constructed to represent either position or harmonic space.
+
+:py:class:`HPSpace` and :py:class:`GLSpace` describe pixelisations of the
+2-sphere; their counterpart in harmonic space is :py:class:`LMSpace`, which
+contains spherical harmonic coefficients.
+
+:py:class:`PowerSpace` is used to describe one-dimensional power spectra.
+
+.. toctree::
+    :maxdepth: 1
+
+    RGSpace                         <../mod/nifty4.domains.rg_space>
+    HPSpace                         <../mod/nifty4.domains.hp_space>
+    GLSpace                         <../mod/nifty4.domains.gl_space>
+    LMSpace                         <../mod/nifty4.domains.lm_space>
+
+    PowerSpace                      <../mod/nifty4.domains.power_space>

docs/source/concepts/operators.rst

@@ -5,22 +5,28 @@ Description of Operators
 
 .. toctree::
     :maxdepth: 1
-    :caption: Types of Operators
+    :caption: Commonly used operators
 
-    Adjoint                             <../mod/nifty4.operators.adjoint_operator>
-    Chain                               <../mod/nifty4.operators.chain_operator>
-    Diagonal                            <../mod/nifty4.operators.diagonal_operator>
-    DOF Projection                      <../mod/nifty4.operators.dof_projection_operator>
-    Endomorphic                         <../mod/nifty4.operators.endomorphic_operator>
-    FFT                                 <../mod/nifty4.operators.fft_operator>
-    FFT Smoothing                       <../mod/nifty4.operators.fft_smoothing_operator>
-    Geometry Remover                    <../mod/nifty4.operators.geometry_remover>
-    Harmonic Transform                  <../mod/nifty4.operators.harmonic_transform_operator>
-    Inverse                             <../mod/nifty4.operators.inverse_operator>
-    Inversion Enabler                   <../mod/nifty4.operators.inversion_enabler>
-    Laplace                             <../mod/nifty4.operators.linear_operator>
-    Linear                              <../mod/nifty4.operators.power_projection_operator>
-    Power Projection                    <../mod/nifty4.operators.power_projection_operator>
-    Scaling                             <../mod/nifty4.operators.smoothness_operator>
-    Smoothness                          <../mod/nifty4.operators.smoothness_operator>
-    Sum                                 <../mod/nifty4.operators.sum_operator>
+    LinearOperator                      <../mod/nifty4.operators.linear_operator>
+    EndomorphicOperator                 <../mod/nifty4.operators.endomorphic_operator>
+    ScalingOperator                     <../mod/nifty4.operators.scaling_operator>
+    DiagonalOperator                    <../mod/nifty4.operators.diagonal_operator>
+    HarmonicTransformOperator           <../mod/nifty4.operators.harmonic_transform_operator>
+    PowerProjectionOperator             <../mod/nifty4.operators.power_projection_operator>
+
+.. toctree::
+    :maxdepth: 1
+    :caption: Not so commonly used operators
+
+    FFTOperator                         <../mod/nifty4.operators.fft_operator>
+    FFTSmoothingOperator                <../mod/nifty4.operators.fft_smoothing_operator>
+    SmoothnessOperator                  <../mod/nifty4.operators.smoothness_operator>
+    InversionEnabler                    <../mod/nifty4.operators.inversion_enabler>
+    GeometryRemover                     <../mod/nifty4.operators.geometry_remover>
+
+..    Adjoint                             <../mod/nifty4.operators.adjoint_operator>
+..    Chain                               <../mod/nifty4.operators.chain_operator>
+..    DOF Projection                      <../mod/nifty4.operators.dof_projection_operator>
+..    Inverse                             <../mod/nifty4.operators.inverse_operator>
+..    Laplace                             <../mod/nifty4.operators.linear_operator>
+..    Sum                                 <../mod/nifty4.operators.sum_operator>

docs/source/start.rst

@@ -41,7 +41,7 @@ In the following sections, the concepts briefly presented here will be discussed
 Domains
 .......
 
-One of the fundamental building blocks of the NIFTy4 framework is the /domain/.
+One of the fundamental building blocks of the NIFTy4 framework is the *domain*.
 Its required capabilities are expressed by the abstract :py:class:`Domain` class.
 A domain must be able to answer the following queries:
 

test/test_energies/test_map.py

@@ -72,7 +72,6 @@ class Energy_Tests(unittest.TestCase):
         tol = 1e-5
         assert_allclose(a, b, rtol=tol, atol=tol)
 
-
     @expand(product([ift.RGSpace(64, distances=.789),
                      ift.RGSpace([32, 32], distances=.789)],
                     [ift.library.Tanh, ift.library.Exponential,