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  <div class="section" id="the-fftoperator-class">
<h1>The <code class="docutils literal"><span class="pre">FFTOperator</span></code> class – …<a class="headerlink" href="#the-fftoperator-class" title="Permalink to this headline"></a></h1>
<dl class="class">
<dt id="nifty.FFTOperator">
<em class="property">class </em><code class="descclassname">nifty.</code><code class="descname">FFTOperator</code><a class="reference internal" href="_modules/nifty/operators/fft_operator/fft_operator.html#FFTOperator"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#nifty.FFTOperator" title="Permalink to this definition"></a></dt>
<dd><p>Bases: <code class="xref py py-class docutils literal"><span class="pre">nifty.operators.linear_operator.linear_operator.LinearOperator</span></code></p>
<p>Transforms between a pair of position and harmonic domains.</p>
<dl class="docutils">
<dt>Built-in domain pairs are</dt>
<dd><ul class="first last simple">
<li>a harmonic and a non-harmonic RGSpace (with matching distances)</li>
<li>a HPSpace and a LMSpace</li>
<li>a GLSpace and a LMSpace</li>
</ul>
</dd>
</dl>
<p>Within a domain pair, both orderings are possible.</p>
<p>The operator provides a “times” and an “adjoint_times” operation.
For a pair of RGSpaces, the “adjoint_times” operation is equivalent to
“inverse_times”; for the sphere-related domains this is not the case, since
the operator matrix is not square.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><p class="first"><strong>domain: Space or single-element tuple of Spaces</strong></p>
<blockquote>
<div><p>The domain of the data that is input by “times” and output by
“adjoint_times”.</p>
</div></blockquote>
<p><strong>target: Space or single-element tuple of Spaces (optional)</strong></p>
<blockquote>
<div><p>The domain of the data that is output by “times” and input by
“adjoint_times”.
If omitted, a co-domain will be chosen automatically.
Whenever “domain” is an RGSpace, the codomain (and its parameters) are
uniquely determined (except for “zerocenter”).
For GLSpace, HPSpace, and LMSpace, a sensible (but not unique)
co-domain is chosen that should work satisfactorily in most situations,
but for full control, the user should explicitly specify a codomain.</p>
</div></blockquote>
<p><strong>module: String (optional)</strong></p>
<blockquote>
<div><p>Software module employed for carrying out the transform operations.
For RGSpace pairs this can be “numpy” or “fftw”, where “numpy” is
always available, but “fftw” offers higher performance and
parallelization. For sphere-related domains, only “pyHealpix” is
available. If omitted, “fftw” is selected for RGSpaces if available,
else “numpy”; on the sphere the default is “pyHealpix”.</p>
</div></blockquote>
<p><strong>domain_dtype: data type (optional)</strong></p>
<blockquote>
<div><p>Data type of the fields that go into “times” and come out of
“adjoint_times”. Default is “numpy.complex”.</p>
</div></blockquote>
<p><strong>target_dtype: data type (optional)</strong></p>
<blockquote>
<div><p>Data type of the fields that go into “adjoint_times” and come out of
“times”. Default is “numpy.complex”.</p>
</div></blockquote>
</td>
</tr>
<tr class="field-even field"><th class="field-name">Raises:</th><td class="field-body"><p class="first"><strong>ValueError:</strong></p>
<blockquote class="last">
<div><p>if “domain” or “target” are not of the proper type.</p>
</div></blockquote>
</td>
</tr>
</tbody>
</table>
<p class="rubric">Attributes</p>
<table border="1" class="docutils">
<colgroup>
<col width="25%" />
<col width="75%" />
</colgroup>
<tbody valign="top">
<tr class="row-odd"><td>domain: Tuple of Spaces (with one entry)</td>
<td>The domain of the data that is input by “times” and output by “adjoint_times”.</td>
</tr>
<tr class="row-even"><td>target: Tuple of Spaces (with one entry)</td>
<td>The domain of the data that is output by “times” and input by “adjoint_times”.</td>
</tr>
<tr class="row-odd"><td>unitary: bool</td>
<td>Returns True if the operator is unitary (currently only the case if the domain and codomain are RGSpaces), else False.</td>
</tr>
</tbody>
</table>
<p class="rubric">Methods</p>
<table border="1" class="longtable docutils">
<colgroup>
<col width="10%" />
<col width="90%" />
</colgroup>
<tbody valign="top">
<tr class="row-odd"><td><a class="reference internal" href="#nifty.FFTOperator.get_default_codomain" title="nifty.FFTOperator.get_default_codomain"><code class="xref py py-obj docutils literal"><span class="pre">get_default_codomain</span></code></a>(domain)</td>
<td>Returns a codomain to the given domain.</td>
</tr>
</tbody>
</table>
<dl class="classmethod">
<dt id="nifty.FFTOperator.get_default_codomain">
<em class="property">classmethod </em><code class="descname">get_default_codomain</code><span class="sig-paren">(</span><em>domain</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/nifty/operators/fft_operator/fft_operator.html#FFTOperator.get_default_codomain"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#nifty.FFTOperator.get_default_codomain" title="Permalink to this definition"></a></dt>
<dd><p>Returns a codomain to the given domain.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><p class="first"><strong>domain: Space</strong></p>
<blockquote>
<div><p>An instance of RGSpace, HPSpace, GLSpace or LMSpace.</p>
</div></blockquote>
</td>
</tr>
<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">target: Space</p>
<blockquote>
<div><p>A (more or less perfect) counterpart to “domain” with respect
to a FFT operation.
Whenever “domain” is an RGSpace, the codomain (and its parameters)
are uniquely determined (except for “zerocenter”).
For GLSpace, HPSpace, and LMSpace, a sensible (but not unique)
co-domain is chosen that should work satisfactorily in most
situations. For full control however, the user should not rely on
this method.</p>
</div></blockquote>
</td>
</tr>
<tr class="field-odd field"><th class="field-name">Raises:</th><td class="field-body"><p class="first"><strong>ValueError:</strong></p>
<blockquote class="last">
<div><p>if no default codomain is defined for “domain”.</p>
</div></blockquote>
</td>
</tr>
</tbody>
</table>
</dd></dl>

<dl class="attribute">
<dt id="nifty.FFTOperator.domain">
<code class="descname">domain</code><a class="headerlink" href="#nifty.FFTOperator.domain" title="Permalink to this definition"></a></dt>
<dd><p><em>domain</em> – tuple of DomainObjects, i.e. Spaces and FieldTypes
The domain on which the Operator’s input Field lives.
Every Operator which inherits from the abstract LinearOperator
base class must have this attribute.</p>
</dd></dl>

<dl class="attribute">
<dt id="nifty.FFTOperator.target">
<code class="descname">target</code><a class="headerlink" href="#nifty.FFTOperator.target" title="Permalink to this definition"></a></dt>
<dd><p><em>target</em> – tuple of DomainObjects, i.e. Spaces and FieldTypes
The domain on which the Operator’s output Field lives.
Every Operator which inherits from the abstract LinearOperator
base class must have this attribute.</p>
</dd></dl>

<dl class="attribute">
<dt id="nifty.FFTOperator.unitary">
<code class="descname">unitary</code><a class="headerlink" href="#nifty.FFTOperator.unitary" title="Permalink to this definition"></a></dt>
<dd><p><em>unitary</em> – boolean
States whether the Operator is unitary or not.
Every Operator which inherits from the abstract LinearOperator
base class must have this attribute.</p>
</dd></dl>

</dd></dl>

</div>


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