Source code for astropy.units.function.logarithmic

# -*- coding: utf-8 -*-
# Licensed under a 3-clause BSD style license - see LICENSE.rst
import numpy as np

from astropy.units import (dimensionless_unscaled, photometric, Unit,
                           CompositeUnit, UnitsError, UnitTypeError,
                           UnitConversionError)

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 : str, `~astropy.units.UnitBase`, or `~astropy.units.function.FunctionUnitBase`, 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 def __pow__(self, other): # We check if this power is OK by applying it first to the unit. try: other = float(other) except TypeError: return NotImplemented new_unit = self.unit ** other new_value = self.view(np.ndarray) ** other return self._new_view(new_value, new_unit) def __ilshift__(self, other): try: other = Unit(other) except UnitTypeError: return NotImplemented if not isinstance(other, self._unit_class): return NotImplemented try: factor = self.unit.physical_unit._to(other.physical_unit) except UnitConversionError: # Maybe via equivalencies? Now we do make a temporary copy. try: value = self._to_value(other) except UnitConversionError: return NotImplemented self.view(np.ndarray)[...] = value else: self.view(np.ndarray)[...] += self.unit.from_physical(factor) self._set_unit(other) 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={}".format(photometric.Bol.si)) m_bol = MagUnit(photometric.bol) m_bol.__doc__ = ("Apparent bolometric magnitude: m_bol=0 corresponds to " "f_bol0={}".format(photometric.bol.si))