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ift
NIFTy
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4a8838e9
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4a8838e9
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Jan 11, 2019
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Martin Reinecke
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@@ -299,62 +299,6 @@ The properties :attr:`~LinearOperator.adjoint` and
were the original operator's adjoint or inverse, respectively.
Operators
=========
Operator classes (represented by NIFTy5's abstract :class:`operators.operator.Operator` class) are used to construct
the equations of a specific inference problem.
Most operators are defined via a position, which is a :class:`~multi_field.MultiField` object,
their value at this position, which is again a :class:`~multi_field.MultiField` object and a Jacobian derivative,
which is a :class:`operators.linear_operator.LinearOperator` and is needed for the minimization procedure.
Using the existing basic operator classes one can construct more complicated operators, as
NIFTy allows for easy and self-consinstent combination via point-wise multiplication,
addition and subtraction. The operator resulting from these operations then automatically
contains the correct Jacobians, positions and values.
Notably, :class:`Constant` and :class:`Variable` allow for an easy way to turn
inference of specific quantities on and off.
The basic operator classes also allow for more complex operations on operators such as
the application of :class:`LinearOperators` or local non-linearities.
As an example one may consider the following combination of ``x``, which is an operator of type
:class:`Variable` and ``y``, which is an operator of type :class:`Constant`::
z = x*x + y
``z`` will then be an operator with the following properties::
z.value = x.value*x.value + y.value
z.position = Union(x.position, y.position)
z.jacobian = 2*makeOp(x.value)
Basic operators
---------------
# FIXME All this is outdated!
Basic operator classes provided by NIFTy are
- :class:`Constant` contains a constant value and has a zero valued Jacobian.
Like other operators, it has a position, but its value does not depend on it.
- :class:`Variable` returns the position as its value, its derivative is one.
- :class:`LinearModel` applies a :class:`operators.linear_operator.LinearOperator` on the model.
- :class:`LocalModel` applies a non-linearity locally on the model.
value and Jacobian are combined into corresponding :class:`MultiFields` and operators.
Advanced operators
------------------
NIFTy also provides a library of more sophisticated operators which are used for more
specific inference problems. Currently these are:
- :class:`AmplitudeOperator`, which returns a smooth power spectrum.
- :class:`InverseGammaOperator`, which models point sources which follow a inverse gamma distribution.
- :class:`CorrelatedField`, which models a diffuse log-normal field. It takes an amplitude operator
to specify the correlation structure of the field.
.. _minimization:
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