harmonic_operators.py 13.7 KB
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# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
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# Copyright(C) 2013-2019 Max-Planck-Society
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#
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# NIFTy is being developed at the Max-Planck-Institut fuer Astrophysik.
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import numpy as np

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from .. import fft, utilities
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from ..domain_tuple import DomainTuple
from ..domains.gl_space import GLSpace
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from ..domains.lm_space import LMSpace
from ..domains.rg_space import RGSpace
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from ..field import Field
from .diagonal_operator import DiagonalOperator
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from .linear_operator import LinearOperator
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from .scaling_operator import ScalingOperator


class FFTOperator(LinearOperator):
    """Transforms between a pair of position and harmonic RGSpaces.

    Parameters
    ----------
    domain: Domain, tuple of Domain or DomainTuple
        The domain of the data that is input by "times" and output by
        "adjoint_times".
    target: Domain, optional
        The target (sub-)domain of the transform operation.
        If omitted, a domain will be chosen automatically.
    space: int, optional
        The index of the subdomain on which the operator should act
        If None, it is set to 0 if `domain` contains exactly one space.
        `domain[space]` must be an RGSpace.

    Notes
    -----
    This operator performs full FFTs, which implies that its output field will
    always have complex type, regardless of the type of the input field.
    If a real field is desired after a forward/backward transform couple, it
    must be manually cast to real.
    """

    def __init__(self, domain, target=None, space=None):
        # Initialize domain and target
        self._domain = DomainTuple.make(domain)
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        self._capability = self._all_ops
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        self._space = utilities.infer_space(self._domain, space)

        adom = self._domain[self._space]
        if not isinstance(adom, RGSpace):
            raise TypeError("FFTOperator only works on RGSpaces")
        if target is None:
            target = adom.get_default_codomain()

        self._target = [dom for dom in self._domain]
        self._target[self._space] = target
        self._target = DomainTuple.make(self._target)
        adom.check_codomain(target)
        target.check_codomain(adom)

    def apply(self, x, mode):
        self._check_input(x, mode)
        ncells = x.domain[self._space].size
        if x.domain[self._space].harmonic:  # harmonic -> position
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            func = fft.ifftn
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            fct = ncells
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        else:
            func = fft.fftn
            fct = 1.
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        axes = x.domain.axes[self._space]
        tdom = self._tgt(mode)
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        tmp = func(x.val, axes=axes)
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        Tval = Field(tdom, tmp)
        if mode & (LinearOperator.TIMES | LinearOperator.ADJOINT_TIMES):
            fct *= self._domain[self._space].scalar_dvol
        else:
            fct *= self._target[self._space].scalar_dvol
        return Tval if fct == 1 else Tval*fct


class HartleyOperator(LinearOperator):
    """Transforms between a pair of position and harmonic RGSpaces.

    Parameters
    ----------
    domain: Domain, tuple of Domain or DomainTuple
        The domain of the data that is input by "times" and output by
        "adjoint_times".
    target: Domain, optional
        The target (sub-)domain of the transform operation.
        If omitted, a domain will be chosen automatically.
    space: int, optional
        The index of the subdomain on which the operator should act
        If None, it is set to 0 if `domain` contains exactly one space.
        `domain[space]` must be an RGSpace.

    Notes
    -----
    This operator always produces output fields with the same data type as
    its input. This is achieved by performing so-called Hartley transforms
    (https://en.wikipedia.org/wiki/Discrete_Hartley_transform).
    For complex input fields, the operator will transform the real and
    imaginary parts separately and use the results as real and imaginary parts
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    of the result field, respectively.
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    In many contexts the Hartley transform is a perfect substitute for the
    Fourier transform, but in some situations (e.g. convolution with a general,
    non-symmetric kernel, the full FFT must be used instead.
    """

    def __init__(self, domain, target=None, space=None):
        # Initialize domain and target
        self._domain = DomainTuple.make(domain)
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        self._capability = self._all_ops
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        self._space = utilities.infer_space(self._domain, space)

        adom = self._domain[self._space]
        if not isinstance(adom, RGSpace):
            raise TypeError("HartleyOperator only works on RGSpaces")
        if target is None:
            target = adom.get_default_codomain()

        self._target = [dom for dom in self._domain]
        self._target[self._space] = target
        self._target = DomainTuple.make(self._target)
        adom.check_codomain(target)
        target.check_codomain(adom)

    def apply(self, x, mode):
        self._check_input(x, mode)
        if utilities.iscomplextype(x.dtype):
            return (self._apply_cartesian(x.real, mode) +
                    1j*self._apply_cartesian(x.imag, mode))
        else:
            return self._apply_cartesian(x, mode)

    def _apply_cartesian(self, x, mode):
        axes = x.domain.axes[self._space]
        tdom = self._tgt(mode)
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        tmp = fft.hartley(x.val, axes=axes)
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        Tval = Field(tdom, tmp)
        if mode & (LinearOperator.TIMES | LinearOperator.ADJOINT_TIMES):
            fct = self._domain[self._space].scalar_dvol
        else:
            fct = self._target[self._space].scalar_dvol
        return Tval if fct == 1 else Tval*fct


class SHTOperator(LinearOperator):
    """Transforms between a harmonic domain on the sphere and a position
    domain counterpart.

    Built-in domain pairs are
      - an LMSpace and a HPSpace
      - an LMSpace and a GLSpace

    The supported operations are times() and adjoint_times().

    Parameters
    ----------
    domain : Domain, tuple of Domain or DomainTuple
        The domain of the data that is input by "times" and output by
        "adjoint_times".
    target : Domain, optional
        The target domain of the transform operation.
        If omitted, a domain will be chosen automatically.
        Whenever the input domain of the transform is an RGSpace, the codomain
        (and its parameters) are uniquely determined.
        For LMSpace, a GLSpace of sufficient resolution is chosen.
    space : int, optional
        The index of the domain on which the operator should act
        If None, it is set to 0 if domain contains exactly one subdomain.
        domain[space] must be a LMSpace.
    """

    def __init__(self, domain, target=None, space=None):
        # Initialize domain and target
        self._domain = DomainTuple.make(domain)
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        self._capability = self.TIMES | self.ADJOINT_TIMES
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        self._space = utilities.infer_space(self._domain, space)

        hspc = self._domain[self._space]
        if not isinstance(hspc, LMSpace):
            raise TypeError("SHTOperator only works on a LMSpace domain")
        if target is None:
            target = hspc.get_default_codomain()

        self._target = [dom for dom in self._domain]
        self._target[self._space] = target
        self._target = DomainTuple.make(self._target)
        hspc.check_codomain(target)
        target.check_codomain(hspc)

        from pyHealpix import sharpjob_d
        self.lmax = hspc.lmax
        self.mmax = hspc.mmax
        self.sjob = sharpjob_d()
        self.sjob.set_triangular_alm_info(self.lmax, self.mmax)
        if isinstance(target, GLSpace):
            self.sjob.set_Gauss_geometry(target.nlat, target.nlon)
        else:
            self.sjob.set_Healpix_geometry(target.nside)

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    def __reduce__(self):
        return (_unpickleSHTOperator,
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                (self._domain, self._target[self._space], self._space))
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    def apply(self, x, mode):
        self._check_input(x, mode)
        if utilities.iscomplextype(x.dtype):
            return (self._apply_spherical(x.real, mode) +
                    1j*self._apply_spherical(x.imag, mode))
        else:
            return self._apply_spherical(x, mode)

    def _slice_p2h(self, inp):
        rr = self.sjob.alm2map_adjoint(inp)
        if len(rr) != ((self.mmax+1)*(self.mmax+2))//2 + \
                      (self.mmax+1)*(self.lmax-self.mmax):
            raise ValueError("array length mismatch")
        res = np.empty(2*len(rr)-self.lmax-1, dtype=rr[0].real.dtype)
        res[0:self.lmax+1] = rr[0:self.lmax+1].real
        res[self.lmax+1::2] = np.sqrt(2)*rr[self.lmax+1:].real
        res[self.lmax+2::2] = np.sqrt(2)*rr[self.lmax+1:].imag
        return res/np.sqrt(np.pi*4)

    def _slice_h2p(self, inp):
        res = np.empty((len(inp)+self.lmax+1)//2, dtype=(inp[0]*1j).dtype)
        if len(res) != ((self.mmax+1)*(self.mmax+2))//2 + \
                       (self.mmax+1)*(self.lmax-self.mmax):
            raise ValueError("array length mismatch")
        res[0:self.lmax+1] = inp[0:self.lmax+1]
        res[self.lmax+1:] = np.sqrt(0.5)*(inp[self.lmax+1::2] +
                                          1j*inp[self.lmax+2::2])
        res = self.sjob.alm2map(res)
        return res/np.sqrt(np.pi*4)

    def _apply_spherical(self, x, mode):
        axes = x.domain.axes[self._space]
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        v = x.val
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        p2h = not x.domain[self._space].harmonic
        tdom = self._tgt(mode)
        func = self._slice_p2h if p2h else self._slice_h2p
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        odat = np.empty(tdom.shape, dtype=x.dtype)
        for slice in utilities.get_slice_list(v.shape, axes):
            odat[slice] = func(v[slice])
        return Field(tdom, odat)
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def _unpickleSHTOperator(*args):
    return SHTOperator(*args)


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class HarmonicTransformOperator(LinearOperator):
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    """Transforms between a harmonic domain and a position domain counterpart.

    Built-in domain pairs are
      - a harmonic and a non-harmonic RGSpace (with matching distances)
      - an LMSpace and a HPSpace
      - an LMSpace and a GLSpace

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    The supported operations are times() and adjoint_times().
    If inverse_times() on RGSpaces is needed the HartleyOperator should be used instead.
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    Parameters
    ----------
    domain : Domain, tuple of Domain or DomainTuple
        The domain of the data that is input by "times" and output by
        "adjoint_times".
    target : Domain, optional
        The target domain of the transform operation.
        If omitted, a domain will be chosen automatically.
        Whenever the input domain of the transform is an RGSpace, the codomain
        (and its parameters) are uniquely determined.
        For LMSpace, a GLSpace of sufficient resolution is chosen.
    space : int, optional
        The index of the domain on which the operator should act
        If None, it is set to 0 if domain contains exactly one subdomain.
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        domain[space] must be a harmonic domain.
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    Notes
    -----
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    HarmonicTransformOperator uses a Hartley transformation to transform
    between harmonic and non-harmonic RGSpaces. This has the advantage that all
    field values are real in either space. If you require a true Fourier
    transform you should use FFTOperator instead.
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    """

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    def __init__(self, domain, target=None, space=None):
        domain = DomainTuple.make(domain)
        space = utilities.infer_space(domain, space)

        hspc = domain[space]
        if not hspc.harmonic:
            raise TypeError(
                "HarmonicTransformOperator only works on a harmonic space")
        if isinstance(hspc, RGSpace):
            self._op = HartleyOperator(domain, target, space)
        else:
            self._op = SHTOperator(domain, target, space)
        self._domain = self._op.domain
        self._target = self._op.target
        self._capability = self.TIMES | self.ADJOINT_TIMES

    def apply(self, x, mode):
        self._check_input(x, mode)
        return self._op.apply(x, mode)
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def HarmonicSmoothingOperator(domain, sigma, space=None):
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    """Returns an operator that carries out a smoothing with a Gaussian kernel
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    of width `sigma` on the part of `domain` given by `space`.
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    Parameters
    ----------
    domain : Domain, tuple of Domain, or DomainTuple
       The total domain of the operator's input and output fields
    sigma : float>=0
       The sigma of the Gaussian used for smoothing. It has the same units as
       the RGSpace the operator is working on.
       If `sigma==0`, an identity operator will be returned.
    space : int, optional
       The index of the sub-domain on which the smoothing is performed.
       Can be omitted if `domain` only has one sub-domain.

    Notes
    -----
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    The sub-domain on which the smoothing is carried out *must* be a
    non-harmonic `RGSpace`.
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    """

    sigma = float(sigma)
    if sigma < 0.:
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        raise ValueError("sigma must be non-negative")
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    if sigma == 0.:
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        return ScalingOperator(domain, 1.)
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    domain = DomainTuple.make(domain)
    space = utilities.infer_space(domain, space)
    if domain[space].harmonic:
        raise TypeError("domain must not be harmonic")
    Hartley = HartleyOperator(domain, space=space)
    codomain = Hartley.domain[space].get_default_codomain()
    kernel = codomain.get_k_length_array()
    smoother = codomain.get_fft_smoothing_kernel_function(sigma)
    kernel = smoother(kernel)
    ddom = list(domain)
    ddom[space] = codomain
    diag = DiagonalOperator(kernel, ddom, space)
    return Hartley.inverse(diag(Hartley))