# -*- coding: utf-8 -*-
# Licensed under a 3-clause BSD style license - see LICENSE.rst
import numpy as np
from astropy.units import CompositeUnit, UnitsError, dimensionless_unscaled, photometric
from .core import FunctionUnitBase, FunctionQuantity
from .units import dex, dB, mag
__all__ = ['LogUnit', 'MagUnit', 'DexUnit', 'DecibelUnit',
'LogQuantity', 'Magnitude', 'Decibel', 'Dex',
'STmag', 'ABmag', 'M_bol', 'm_bol']
[docs]class LogUnit(FunctionUnitBase):
"""Logarithmic unit containing a physical one
Usually, logarithmic units are instantiated via specific subclasses
such `MagUnit`, `DecibelUnit`, and `DexUnit`.
Parameters
----------
physical_unit : `~astropy.units.Unit` or `string`
Unit that is encapsulated within the logarithmic function unit.
If not given, dimensionless.
function_unit : `~astropy.units.Unit` or `string`
By default, the same as the logarithmic unit set by the subclass.
"""
# the four essential overrides of FunctionUnitBase
@property
def _default_function_unit(self):
return dex
@property
def _quantity_class(self):
return LogQuantity
[docs] def from_physical(self, x):
"""Transformation from value in physical to value in logarithmic units.
Used in equivalency."""
return dex.to(self._function_unit, np.log10(x))
[docs] def to_physical(self, x):
"""Transformation from value in logarithmic to value in physical units.
Used in equivalency."""
return 10 ** self._function_unit.to(dex, x)
# ^^^^ the four essential overrides of FunctionUnitBase
# add addition and subtraction, which imply multiplication/division of
# the underlying physical units
def _add_and_adjust_physical_unit(self, other, sign_self, sign_other):
"""Add/subtract LogUnit to/from another unit, and adjust physical unit.
self and other are multiplied by sign_self and sign_other, resp.
We wish to do: ±lu_1 + ±lu_2 -> lu_f (lu=logarithmic unit)
and pu_1^(±1) * pu_2^(±1) -> pu_f (pu=physical unit)
Raises
------
UnitsError
If function units are not equivalent.
"""
# First, insist on compatible logarithmic type. Here, plain u.mag,
# u.dex, and u.dB are OK, i.e., other does not have to be LogUnit
# (this will indirectly test whether other is a unit at all).
try:
getattr(other, 'function_unit', other)._to(self._function_unit)
except AttributeError:
# if other is not a unit (i.e., does not have _to).
return NotImplemented
except UnitsError:
raise UnitsError("Can only add/subtract logarithmic units of"
"of compatible type.")
other_physical_unit = getattr(other, 'physical_unit',
dimensionless_unscaled)
physical_unit = CompositeUnit(
1, [self._physical_unit, other_physical_unit],
[sign_self, sign_other])
return self._copy(physical_unit)
def __neg__(self):
return self._copy(self.physical_unit**(-1))
def __add__(self, other):
# Only know how to add to a logarithmic unit with compatible type,
# be it a plain one (u.mag, etc.,) or another LogUnit
return self._add_and_adjust_physical_unit(other, +1, +1)
def __radd__(self, other):
return self._add_and_adjust_physical_unit(other, +1, +1)
def __sub__(self, other):
return self._add_and_adjust_physical_unit(other, +1, -1)
def __rsub__(self, other):
# here, in normal usage other cannot be LogUnit; only equivalent one
# would be u.mag,u.dB,u.dex. But might as well use common routine.
return self._add_and_adjust_physical_unit(other, -1, +1)
[docs]class MagUnit(LogUnit):
"""Logarithmic physical units expressed in magnitudes
Parameters
----------
physical_unit : `~astropy.units.Unit` or `string`
Unit that is encapsulated within the magnitude function unit.
If not given, dimensionless.
function_unit : `~astropy.units.Unit` or `string`
By default, this is ``mag``, but this allows one to use an equivalent
unit such as ``2 mag``.
"""
@property
def _default_function_unit(self):
return mag
@property
def _quantity_class(self):
return Magnitude
[docs]class DexUnit(LogUnit):
"""Logarithmic physical units expressed in magnitudes
Parameters
----------
physical_unit : `~astropy.units.Unit` or `string`
Unit that is encapsulated within the magnitude function unit.
If not given, dimensionless.
function_unit : `~astropy.units.Unit` or `string`
By default, this is ``dex`, but this allows one to use an equivalent
unit such as ``0.5 dex``.
"""
@property
def _default_function_unit(self):
return dex
@property
def _quantity_class(self):
return Dex
[docs]class DecibelUnit(LogUnit):
"""Logarithmic physical units expressed in dB
Parameters
----------
physical_unit : `~astropy.units.Unit` or `string`
Unit that is encapsulated within the decibel function unit.
If not given, dimensionless.
function_unit : `~astropy.units.Unit` or `string`
By default, this is ``dB``, but this allows one to use an equivalent
unit such as ``2 dB``.
"""
@property
def _default_function_unit(self):
return dB
@property
def _quantity_class(self):
return Decibel
[docs]class LogQuantity(FunctionQuantity):
"""A representation of a (scaled) logarithm of a number with a unit
Parameters
----------
value : number, `~astropy.units.Quantity`, `~astropy.units.function.logarithmic.LogQuantity`, or sequence of convertible items.
The numerical value of the logarithmic quantity. If a number or
a `~astropy.units.Quantity` with a logarithmic unit, it will be
converted to ``unit`` and the physical unit will be inferred from
``unit``. If a `~astropy.units.Quantity` with just a physical unit,
it will converted to the logarithmic unit, after, if necessary,
converting it to the physical unit inferred from ``unit``.
unit : string, `~astropy.units.UnitBase` or `~astropy.units.function.FunctionUnitBase` instance, optional
For an `~astropy.units.function.FunctionUnitBase` instance, the
physical unit will be taken from it; for other input, it will be
inferred from ``value``. By default, ``unit`` is set by the subclass.
dtype : `~numpy.dtype`, optional
The ``dtype`` of the resulting Numpy array or scalar that will
hold the value. If not provided, is is determined automatically
from the input value.
copy : bool, optional
If `True` (default), then the value is copied. Otherwise, a copy will
only be made if ``__array__`` returns a copy, if value is a nested
sequence, or if a copy is needed to satisfy an explicitly given
``dtype``. (The `False` option is intended mostly for internal use,
to speed up initialization where a copy is known to have been made.
Use with care.)
Examples
--------
Typically, use is made of an `~astropy.units.function.FunctionQuantity`
subclass, as in::
>>> import astropy.units as u
>>> u.Magnitude(-2.5)
<Magnitude -2.5 mag>
>>> u.Magnitude(10.*u.count/u.second)
<Magnitude -2.5 mag(ct / s)>
>>> u.Decibel(1.*u.W, u.DecibelUnit(u.mW)) # doctest: +FLOAT_CMP
<Decibel 30. dB(mW)>
"""
# only override of FunctionQuantity
_unit_class = LogUnit
# additions that work just for logarithmic units
def __add__(self, other):
# Add function units, thus multiplying physical units. If no unit is
# given, assume dimensionless_unscaled; this will give the appropriate
# exception in LogUnit.__add__.
new_unit = self.unit + getattr(other, 'unit', dimensionless_unscaled)
# Add actual logarithmic values, rescaling, e.g., dB -> dex.
result = self._function_view + getattr(other, '_function_view', other)
return self._new_view(result, new_unit)
def __radd__(self, other):
return self.__add__(other)
def __iadd__(self, other):
new_unit = self.unit + getattr(other, 'unit', dimensionless_unscaled)
# Do calculation in-place using _function_view of array.
function_view = self._function_view
function_view += getattr(other, '_function_view', other)
self._set_unit(new_unit)
return self
def __sub__(self, other):
# Subtract function units, thus dividing physical units.
new_unit = self.unit - getattr(other, 'unit', dimensionless_unscaled)
# Subtract actual logarithmic values, rescaling, e.g., dB -> dex.
result = self._function_view - getattr(other, '_function_view', other)
return self._new_view(result, new_unit)
def __rsub__(self, other):
new_unit = self.unit.__rsub__(
getattr(other, 'unit', dimensionless_unscaled))
result = self._function_view.__rsub__(
getattr(other, '_function_view', other))
# Ensure the result is in right function unit scale
# (with rsub, this does not have to be one's own).
result = result.to(new_unit.function_unit)
return self._new_view(result, new_unit)
def __isub__(self, other):
new_unit = self.unit - getattr(other, 'unit', dimensionless_unscaled)
# Do calculation in-place using _function_view of array.
function_view = self._function_view
function_view -= getattr(other, '_function_view', other)
self._set_unit(new_unit)
return self
# Could add __mul__ and __div__ and try interpreting other as a power,
# but this seems just too error-prone.
# Methods that do not work for function units generally but are OK for
# logarithmic units as they imply differences and independence of
# physical unit.
[docs] def var(self, axis=None, dtype=None, out=None, ddof=0):
return self._wrap_function(np.var, axis, dtype, out=out, ddof=ddof,
unit=self.unit.function_unit**2)
[docs] def std(self, axis=None, dtype=None, out=None, ddof=0):
return self._wrap_function(np.std, axis, dtype, out=out, ddof=ddof,
unit=self.unit._copy(dimensionless_unscaled))
[docs] def ptp(self, axis=None, out=None):
return self._wrap_function(np.ptp, axis, out=out,
unit=self.unit._copy(dimensionless_unscaled))
[docs] def diff(self, n=1, axis=-1):
return self._wrap_function(np.diff, n, axis,
unit=self.unit._copy(dimensionless_unscaled))
[docs] def ediff1d(self, to_end=None, to_begin=None):
return self._wrap_function(np.ediff1d, to_end, to_begin,
unit=self.unit._copy(dimensionless_unscaled))
_supported_functions = (FunctionQuantity._supported_functions |
set(getattr(np, function) for function in
('var', 'std', 'ptp', 'diff', 'ediff1d')))
[docs]class Dex(LogQuantity):
_unit_class = DexUnit
[docs]class Decibel(LogQuantity):
_unit_class = DecibelUnit
[docs]class Magnitude(LogQuantity):
_unit_class = MagUnit
dex._function_unit_class = DexUnit
dB._function_unit_class = DecibelUnit
mag._function_unit_class = MagUnit
STmag = MagUnit(photometric.STflux)
STmag.__doc__ = "ST magnitude: STmag=-21.1 corresponds to 1 erg/s/cm2/A"
ABmag = MagUnit(photometric.ABflux)
ABmag.__doc__ = "AB magnitude: ABmag=-48.6 corresponds to 1 erg/s/cm2/Hz"
M_bol = MagUnit(photometric.Bol)
M_bol.__doc__ = ("Absolute bolometric magnitude: M_bol=0 corresponds to "
"L_bol0={0}".format(photometric.Bol.si))
m_bol = MagUnit(photometric.bol)
m_bol.__doc__ = ("Apparent bolometric magnitude: m_bol=0 corresponds to "
"f_bol0={0}".format(photometric.bol.si))