Commit a94f7c68 authored by Lukas Platz's avatar Lukas Platz
Browse files

code: added clarifications, fixed minor stuff. index: added clarifications

parent ecedc71f
......@@ -41,7 +41,6 @@ Abstract base class
One of the fundamental building blocks of the NIFTy5 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:
m
- its total number of data entries (pixels), which is accessible via the
:attr:`~Domain.size` property
......@@ -129,7 +128,7 @@ specify full field domains. In principle, a :class:`~domain_tuple.DomainTuple`
can even be empty, which implies that the field living on it is a scalar.
A :class:`~domain_tuple.DomainTuple` supports iteration and indexing, and also
provides the properties :attr:`~domain_tuple.DomainTuple.shape`,
provides the properties :attr:`~domain_tuple.DomainTuple.shape` and
:attr:`~domain_tuple.DomainTuple.size` in analogy to the elementary
:class:`~domains.domain.Domain`.
......@@ -158,11 +157,12 @@ fields with equal domains, or a field and a scalar.
Contractions (like summation, integration, minimum/maximum, computation of
statistical moments) can be carried out either over an entire field (producing
a scalar result) or over sub-domains (resulting in a field defined on a smaller
domain). Scalar products of two fields can also be computed easily.
domain). Scalar products of two fields can also be computed easily. See the
documentation of :class:`~field.Field` for details.
There is also a set of convenience functions to generate fields with constant
values or fields filled with random numbers according to a user-specified
distribution.
distribution: :attr:`~sugar.full`, :attr:`~sugar.from_random`.
Like almost all NIFTy objects, fields are immutable: their value or any other
attribute cannot be modified after construction. To manipulate a field in ways
......@@ -311,11 +311,15 @@ and ``f1`` and ``f2`` are of type :class:`~field.Field`, writing::
will perform the operation suggested intuitively by the notation, checking
domain compatibility while building the composed operator.
The combined operator infers its domain and target from its constituents,
as well as the set of operations it can support.
The properties :attr:`~LinearOperator.adjoint` and
:attr:`~LinearOperator.inverse` return a new operator which behaves as if it
were the original operator's adjoint or inverse, respectively.
The combined operator infers its domain and target from its constituents,
as well as the set of operations it can support.
Instantiating operator adjoints or inverses by :attr:`~LinearOperator.adjoint`
and similar methods is to be distinguished from the instant application of
operators performed by :attr:`~LinearOperator.adjoint_times` and similar
methods.
.. _minimization:
......@@ -368,8 +372,8 @@ failure.
Sensible stopping criteria can vary significantly with the problem being
solved; NIFTy provides one concrete sub-class of :class:`IterationController`
called :class:`GradientNormController`, which should be appropriate in many
circumstances, but users have complete freedom to implement custom sub-classes
for their specific applications.
circumstances, but users have complete freedom to implement custom
:class:`IterationController` sub-classes for their specific applications.
Minimization algorithms
......@@ -424,11 +428,13 @@ the information propagator whose inverse is defined as:
:math:`D^{-1} = \left(R^\dagger N^{-1} R + S^{-1}\right)`.
It needs to be applied in forward direction in order to calculate the Wiener
filter solution. Only its inverse application is straightforward; to use it in
forward direction, we make use of NIFTy's
filter solution, but only its inverse application is straightforward.
To use it in forward direction, we make use of NIFTy's
:class:`~operators.inversion_enabler.InversionEnabler` class, which internally
performs a minimization of a
:class:`~minimization.quadratic_energy.QuadraticEnergy` by means of the
:class:`~minimization.conjugate_gradient.ConjugateGradient` algorithm. An
example is provided in
does the inverse application of the given operator :math:`x = Op^{-1} (y)` by
solving the equation :math:`y = Op (x)` for :math:`x`.
This is accomplished by minimizing a suitable
:class:`~minimization.quadratic_energy.QuadraticEnergy`
with the :class:`~minimization.conjugate_gradient.ConjugateGradient`
algorithm. An example is provided in
:func:`~library.wiener_filter_curvature.WienerFilterCurvature`.
NIFTy -- Numerical Information Field Theory
===========================================
**NIFTy** [1]_, [2]_, "\ **N**\umerical **I**\nformation **F**\ield **T**\heor\ **y**\ ", is a versatile library designed to enable the development of signal inference algorithms that are independent of the underlying spatial grid and its resolution.
**NIFTy** [1]_, [2]_, "\ **N**\umerical **I**\nformation **F**\ield **T**\heor\ **y**\ ", is a versatile library designed to enable the development of signal inference algorithms that are independent of the underlying grids (spatial, spectral, temporal, …) and their resolutions.
Its object-oriented framework is written in Python, although it accesses libraries written in C++ and C for efficiency.
NIFTy offers a toolkit that abstracts discretized representations of continuous spaces, fields in these spaces, and operators acting on fields into classes.
Thereby, the correct normalization of operations on fields is taken care of automatically without concerning the user.
This allows for an abstract formulation and programming of inference algorithms, including those derived within information field theory.
Thus, NIFTy permits its user to rapidly prototype algorithms in 1D and then apply the developed code in higher-dimensional settings to real world problems.
Thus, NIFTy permits its user to rapidly prototype algorithms in 1D or 2D and then apply the developed code in higher-dimensional settings to real world problems.
The set of spaces on which NIFTy operates comprises point sets, *n*-dimensional regular grids, spherical spaces, their harmonic counterparts, and product spaces constructed as combinations of those.
References
......
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