Models and Fitting (astropy.modeling
)¶
Introduction¶
astropy.modeling
provides a framework for representing models and performing
model evaluation and fitting. It currently supports 1-D and 2-D models and
fitting with parameter constraints.
It is designed to be easily extensible and flexible. Models do not reference fitting algorithms explicitly and new fitting algorithms may be added without changing the existing models (though not all models can be used with all fitting algorithms due to constraints such as model linearity).
The goal is to eventually provide a rich toolset of models and fitters such that most users will not need to define new model classes, nor special purpose fitting routines (while making it reasonably easy to do when necessary).
Note
astropy.modeling
is currently a work-in-progress, and thus it is likely
there will still be API changes in later versions of Astropy. Backwards
compatibility support between versions will still be maintained as much as
possible, but new features and enhancements are coming in future versions.
If you have specific ideas for how it might be improved, feel free to let
us know on the astropy-dev mailing list or at
http://feedback.astropy.org
Getting started¶
The examples here use the predefined models and assume the following modules have been imported:
>>> import numpy as np
>>> from astropy.modeling import models, fitting
Using Models¶
The astropy.modeling
package defines a number of models that are collected
under a single namespace as astropy.modeling.models
. Models behave like
parametrized functions:
>>> from astropy.modeling import models
>>> g = models.Gaussian1D(amplitude=1.2, mean=0.9, stddev=0.5)
>>> print(g)
Model: Gaussian1D
Inputs: ('x',)
Outputs: ('y',)
Model set size: 1
Parameters:
amplitude mean stddev
--------- ---- ------
1.2 0.9 0.5
Model parameters can be accessed as attributes:
>>> g.amplitude
Parameter('amplitude', value=1.2)
>>> g.mean
Parameter('mean', value=0.9)
>>> g.stddev
Parameter('stddev', value=0.5, bounds=(1.1754943508222875e-38, None))
and can also be updated via those attributes:
>>> g.amplitude = 0.8
>>> g.amplitude
Parameter('amplitude', value=0.8)
Models can be evaluated by calling them as functions:
>>> g(0.1)
0.22242984036255528
>>> g(np.linspace(0.5, 1.5, 7))
array([0.58091923, 0.71746405, 0.7929204 , 0.78415894, 0.69394278,
0.54952605, 0.3894018 ])
As the above example demonstrates, in general most models evaluate array-like inputs according to the standard Numpy broadcasting rules for arrays.
Models can therefore already be useful to evaluate common functions, independently of the fitting features of the package.
Simple 1-D model fitting¶
In this section, we look at a simple example of fitting a Gaussian to a
simulated dataset. We use the Gaussian1D
and Trapezoid1D
models and the
LevMarLSQFitter
fitter to fit the data:
import numpy as np
import matplotlib.pyplot as plt
from astropy.modeling import models, fitting
# Generate fake data
np.random.seed(0)
x = np.linspace(-5., 5., 200)
y = 3 * np.exp(-0.5 * (x - 1.3)**2 / 0.8**2)
y += np.random.normal(0., 0.2, x.shape)
# Fit the data using a box model.
# Bounds are not really needed but included here to demonstrate usage.
t_init = models.Trapezoid1D(amplitude=1., x_0=0., width=1., slope=0.5,
bounds={"x_0": (-5., 5.)})
fit_t = fitting.LevMarLSQFitter()
t = fit_t(t_init, x, y)
# Fit the data using a Gaussian
g_init = models.Gaussian1D(amplitude=1., mean=0, stddev=1.)
fit_g = fitting.LevMarLSQFitter()
g = fit_g(g_init, x, y)
# Plot the data with the best-fit model
plt.figure(figsize=(8,5))
plt.plot(x, y, 'ko')
plt.plot(x, t(x), label='Trapezoid')
plt.plot(x, g(x), label='Gaussian')
plt.xlabel('Position')
plt.ylabel('Flux')
plt.legend(loc=2)
()
As shown above, once instantiated, the fitter class can be used as a function
that takes the initial model (t_init
or g_init
) and the data values
(x
and y
), and returns a fitted model (t
or g
).
Simple 2-D model fitting¶
Similarly to the 1-D example, we can create a simulated 2-D data dataset, and fit a polynomial model to it. This could be used for example to fit the background in an image.
import warnings
import numpy as np
import matplotlib.pyplot as plt
from astropy.modeling import models, fitting
# Generate fake data
np.random.seed(0)
y, x = np.mgrid[:128, :128]
z = 2. * x ** 2 - 0.5 * x ** 2 + 1.5 * x * y - 1.
z += np.random.normal(0., 0.1, z.shape) * 50000.
# Fit the data using astropy.modeling
p_init = models.Polynomial2D(degree=2)
fit_p = fitting.LevMarLSQFitter()
with warnings.catch_warnings():
# Ignore model linearity warning from the fitter
warnings.simplefilter('ignore')
p = fit_p(p_init, x, y, z)
# Plot the data with the best-fit model
plt.figure(figsize=(8, 2.5))
plt.subplot(1, 3, 1)
plt.imshow(z, origin='lower', interpolation='nearest', vmin=-1e4, vmax=5e4)
plt.title("Data")
plt.subplot(1, 3, 2)
plt.imshow(p(x, y), origin='lower', interpolation='nearest', vmin=-1e4,
vmax=5e4)
plt.title("Model")
plt.subplot(1, 3, 3)
plt.imshow(z - p(x, y), origin='lower', interpolation='nearest', vmin=-1e4,
vmax=5e4)
plt.title("Residual")
()
A list of models is provided in the Reference/API section. The fitting framework includes many useful features that are not demonstrated here, such as weighting of datapoints, fixing or linking parameters, and placing lower or upper limits on parameters. For more information on these, take a look at the Fitting Models to Data documentation.
Model sets¶
In some cases it is necessary to describe many models of the same type but with
different sets of parameter values. This could be done simply by instantiating
as many instances of a Model
as are needed. But that can
be inefficient for a large number of models. To that end, all model classes in
astropy.modeling
can also be used to represent a model set which is a
collection of models of the same type, but with different values for their
parameters.
To instantiate a model set, use argument n_models=N
where N
is the
number of models in the set when constructing the model. The value of each
parameter must be a list or array of length N
, such that each item in
the array corresponds to one model in the set:
>>> g = models.Gaussian1D(amplitude=[1, 2], mean=[0, 0],
... stddev=[0.1, 0.2], n_models=2)
>>> print(g)
Model: Gaussian1D
Inputs: ('x',)
Outputs: ('y',)
Model set size: 2
Parameters:
amplitude mean stddev
--------- ---- ------
1.0 0.0 0.1
2.0 0.0 0.2
This is equivalent to two Gaussians with the parameters amplitude=1, mean=0,
stddev=0.1
and amplitude=2, mean=0, stddev=0.2
respectively. When
printing the model the parameter values are displayed as a table, with each row
corresponding to a single model in the set.
The number of models in a model set can be determined using the len
builtin:
>>> len(g)
2
Single models have a length of 1, and are not considered a model set as such.
When evaluating a model set, by default the input must be the same length as the number of models, with one input per model:
>>> g([0, 0.1])
array([1. , 1.76499381])
The result is an array with one result per model in the set. It is also possible to broadcast a single value to all models in the set:
>>> g(0)
array([1., 2.])
Model sets are used primarily for fitting, allowing a large number of models of the same type to be fitted simultaneously (and independently from each other) to some large set of inputs. For example, fitting a polynomial to the time response of each pixel in a data cube. This can greatly speed up the fitting process, especially for linear models.
Compound models¶
New in version 1.0: This feature is experimental and expected to see significant further development, but the basic usage is stable and expected to see wide use.
While the Astropy modeling package makes it very easy to define new
models either from existing functions, or by writing a
Model
subclass, an additional way to create new models is
by combining them using arithmetic expressions. This works with models built
into Astropy, and most user-defined models as well. For example, it is
possible to create a superposition of two Gaussians like so:
>>> from astropy.modeling import models
>>> g1 = models.Gaussian1D(1, 0, 0.2)
>>> g2 = models.Gaussian1D(2.5, 0.5, 0.1)
>>> g1_plus_2 = g1 + g2
The resulting object g1_plus_2
is itself a new model. Evaluating, say,
g1_plus_2(0.25)
is the same as evaluating g1(0.25) + g2(0.25)
:
>>> g1_plus_2(0.25)
0.5676756958301329
>>> g1_plus_2(0.25) == g1(0.25) + g2(0.25)
True
This model can be further combined with other models in new expressions. It is also possible to define entire new model classes using arithmetic expressions of other model classes. This allows general compound models to be created without specifying any parameter values up front. This more advanced usage is explained in more detail in the compound model documentation.
These new compound models can also be fitted to data, like most other models (though this currently requires one of the non-linear fitters):
import numpy as np
import matplotlib.pyplot as plt
from astropy.modeling import models, fitting
# Generate fake data
np.random.seed(42)
g1 = models.Gaussian1D(1, 0, 0.2)
g2 = models.Gaussian1D(2.5, 0.5, 0.1)
x = np.linspace(-1, 1, 200)
y = g1(x) + g2(x) + np.random.normal(0., 0.2, x.shape)
# Now to fit the data create a new superposition with initial
# guesses for the parameters:
gg_init = models.Gaussian1D(1, 0, 0.1) + models.Gaussian1D(2, 0.5, 0.1)
fitter = fitting.SLSQPLSQFitter()
gg_fit = fitter(gg_init, x, y)
# Plot the data with the best-fit model
plt.figure(figsize=(8,5))
plt.plot(x, y, 'ko')
plt.plot(x, gg_fit(x))
plt.xlabel('Position')
plt.ylabel('Flux')
()
This works for 1-D models, 2-D models, and combinations thereof, though there are some complexities involved in correctly matching up the inputs and outputs of all models used to build a compound model. You can learn more details in the Compound Models documentation.
Astropy models also support convolution through the function
convolve_models
, which returns a compound model.
For instance, the convolution of two Gaussian functions is also a Gaussian function in which the resulting mean (variance) is the sum of the means (variances) of each Gaussian.
import numpy as np
import matplotlib.pyplot as plt
from astropy.modeling import models
from astropy.convolution import convolve_models
g1 = models.Gaussian1D(1, -1, 1)
g2 = models.Gaussian1D(1, 1, 1)
g3 = convolve_models(g1, g2)
x = np.linspace(-3, 3, 50)
plt.plot(x, g1(x), 'k-')
plt.plot(x, g2(x), 'k-')
plt.plot(x, g3(x), 'k-')
()
Fitting masked data¶
New in version 2.0.4.
When astropy.modeling.fitting.LinearLSQFitter
is provided with the dependent
co-ordinate values as a numpy.ma.MaskedArray
, it ignores any masked values
when performing the fit:
>>> p_init = models.Polynomial1D(degree=1)
>>> x = np.arange(10)
>>> y = np.ma.masked_array(2*x+1, mask=np.zeros_like(x))
>>> y[7] = 100. # simulate spurious value
>>> y.mask[7] = True
>>> fitter = fitting.LinearLSQFitter()
>>> p = fitter(p_init, x, y)
>>> print('Fit intercept={:.3f}, slope={:.3f}'.format(p.c0.value, p.c1.value))
Fit intercept=1.000, slope=2.000
At present, the non-linear fitters do not distinguish between good and bad values in this way.
Note that model set fitting is currently about an order of magnitude slower in
the presence of masked values, because the matrix equation has to be solved for
each model separately, on their respective co-ordinate grids. This is still an
order of magnitude faster than fitting separate model instances, however.
Supplying a numpy.ma.MaskedArray
without any bad (True
) mask values
produces the normal, faster behavior.
Using astropy.modeling
¶
Performance Tips¶
Initializing a compound model with many constituent models can be time consuming. If your code uses the same compound model repeatedly consider initializing it once and reusing the model.
Consider the performance tips that apply to quantities when initializing and evaluating models with quantities.
Reference/API¶
astropy.modeling Package¶
This subpackage provides a framework for representing models and performing model evaluation and fitting. It supports 1D and 2D models and fitting with parameter constraints. It has some predefined models and fitting routines.
Functions¶
custom_model (*args[, fit_deriv]) |
Create a model from a user defined function. |
is_separable (transform) |
A separability test for the outputs of a transform. |
separability_matrix (transform) |
Compute the correlation between outputs and inputs. |
Classes¶
Fittable1DModel (*args[, meta, name]) |
Base class for one-dimensional fittable models. |
Fittable2DModel (*args[, meta, name]) |
Base class for two-dimensional fittable models. |
FittableModel (*args[, meta, name]) |
Base class for models that can be fitted using the built-in fitting algorithms. |
InputParameterError |
Used for incorrect input parameter values and definitions. |
Model (*args[, meta, name]) |
Base class for all models. |
ModelDefinitionError |
Used for incorrect models definitions |
Parameter ([name, description, default, …]) |
Wraps individual parameters. |
ParameterError |
Generic exception class for all exceptions pertaining to Parameters. |
Class Inheritance Diagram¶
astropy.modeling.functional_models Module¶
Mathematical models.
Classes¶
AiryDisk2D ([amplitude, x_0, y_0, radius]) |
Two dimensional Airy disk model. |
Moffat1D ([amplitude, x_0, gamma, alpha]) |
One dimensional Moffat model. |
Moffat2D ([amplitude, x_0, y_0, gamma, alpha]) |
Two dimensional Moffat model. |
Box1D ([amplitude, x_0, width]) |
One dimensional Box model. |
Box2D ([amplitude, x_0, y_0, x_width, y_width]) |
Two dimensional Box model. |
Const1D ([amplitude]) |
One dimensional Constant model. |
Const2D ([amplitude]) |
Two dimensional Constant model. |
Ellipse2D ([amplitude, x_0, y_0, a, b, theta]) |
A 2D Ellipse model. |
Disk2D ([amplitude, x_0, y_0, R_0]) |
Two dimensional radial symmetric Disk model. |
Gaussian1D ([amplitude, mean, stddev]) |
One dimensional Gaussian model. |
Gaussian2D ([amplitude, x_mean, y_mean, …]) |
Two dimensional Gaussian model. |
Linear1D ([slope, intercept]) |
One dimensional Line model. |
Lorentz1D ([amplitude, x_0, fwhm]) |
One dimensional Lorentzian model. |
MexicanHat1D ([amplitude, x_0, sigma]) |
One dimensional Mexican Hat model. |
MexicanHat2D ([amplitude, x_0, y_0, sigma]) |
Two dimensional symmetric Mexican Hat model. |
RedshiftScaleFactor ([z]) |
One dimensional redshift scale factor model. |
Scale ([factor]) |
Multiply a model by a dimensionless factor. |
Multiply ([factor]) |
Multiply a model by a quantity or number. |
Sersic1D ([amplitude, r_eff, n]) |
One dimensional Sersic surface brightness profile. |
Sersic2D ([amplitude, r_eff, n, x_0, y_0, …]) |
Two dimensional Sersic surface brightness profile. |
Shift ([offset]) |
Shift a coordinate. |
Sine1D ([amplitude, frequency, phase]) |
One dimensional Sine model. |
Trapezoid1D ([amplitude, x_0, width, slope]) |
One dimensional Trapezoid model. |
TrapezoidDisk2D ([amplitude, x_0, y_0, R_0, …]) |
Two dimensional circular Trapezoid model. |
Ring2D ([amplitude, x_0, y_0, r_in, width, r_out]) |
Two dimensional radial symmetric Ring model. |
Voigt1D ([x_0, amplitude_L, fwhm_L, fwhm_G]) |
One dimensional model for the Voigt profile. |
Class Inheritance Diagram¶
astropy.modeling.powerlaws Module¶
Power law model variants
Classes¶
PowerLaw1D ([amplitude, x_0, alpha]) |
One dimensional power law model. |
BrokenPowerLaw1D ([amplitude, x_break, …]) |
One dimensional power law model with a break. |
SmoothlyBrokenPowerLaw1D ([amplitude, …]) |
One dimensional smoothly broken power law model. |
ExponentialCutoffPowerLaw1D ([amplitude, …]) |
One dimensional power law model with an exponential cutoff. |
LogParabola1D ([amplitude, x_0, alpha, beta]) |
One dimensional log parabola model (sometimes called curved power law). |
Class Inheritance Diagram¶
astropy.modeling.blackbody Module¶
Model and functions related to blackbody radiation.
Blackbody Radiation¶
Blackbody flux is calculated with Planck law (Rybicki & Lightman 1979):
where the unit of \(B_{\lambda}(T)\) is
\(erg \; s^{-1} cm^{-2} \mathring{A}^{-1} sr^{-1}\), and
\(B_{\nu}(T)\) is \(erg \; s^{-1} cm^{-2} Hz^{-1} sr^{-1}\).
blackbody_lambda()
and
blackbody_nu()
calculate the
blackbody flux for \(B_{\lambda}(T)\) and \(B_{\nu}(T)\),
respectively.
For blackbody representation as a model, see BlackBody1D
.
Examples¶
>>> import numpy as np
>>> from astropy import units as u
>>> from astropy.modeling.blackbody import blackbody_lambda, blackbody_nu
Calculate blackbody flux for 5000 K at 100 and 10000 Angstrom while suppressing any Numpy warnings:
>>> wavelengths = [100, 10000] * u.AA
>>> temperature = 5000 * u.K
>>> with np.errstate(all='ignore'):
... flux_lam = blackbody_lambda(wavelengths, temperature)
... flux_nu = blackbody_nu(wavelengths, temperature)
>>> flux_lam # doctest: +FLOAT_CMP
<Quantity [ 1.27452545e-108, 7.10190526e+005] erg / (Angstrom cm2 s sr)>
>>> flux_nu # doctest: +FLOAT_CMP
<Quantity [ 4.25135927e-123, 2.36894060e-005] erg / (cm2 Hz s sr)>
Plot a blackbody spectrum for 5000 K:
()
Note that an array of temperatures can also be given instead of a single
temperature. In this case, the Numpy broadcasting rules apply: for instance, if
the frequency and temperature have the same shape, the output will have this
shape too, while if the frequency is a 2-d array with shape (n, m)
and the
temperature is an array with shape (m,)
, the output will have a shape
(n, m)
.
See Also¶
Rybicki, G. B., & Lightman, A. P. 1979, Radiative Processes in Astrophysics (New York, NY: Wiley)
Functions¶
blackbody_nu (in_x, temperature) |
Calculate blackbody flux per steradian, \(B_{\nu}(T)\). |
blackbody_lambda (in_x, temperature) |
Like blackbody_nu() but for \(B_{\lambda}(T)\). |
Classes¶
BlackBody1D ([temperature, bolometric_flux]) |
One dimensional blackbody model. |
Class Inheritance Diagram¶
astropy.modeling.polynomial Module¶
This module contains models representing polynomials and polynomial series.
Classes¶
Chebyshev1D (degree[, domain, window, …]) |
Univariate Chebyshev series. |
Chebyshev2D (x_degree, y_degree[, x_domain, …]) |
Bivariate Chebyshev series.. |
Hermite1D (degree[, domain, window, …]) |
Univariate Hermite series. |
Hermite2D (x_degree, y_degree[, x_domain, …]) |
Bivariate Hermite series. |
InverseSIP (ap_order, bp_order[, ap_coeff, …]) |
Inverse Simple Imaging Polynomial |
Legendre1D (degree[, domain, window, …]) |
Univariate Legendre series. |
Legendre2D (x_degree, y_degree[, x_domain, …]) |
Bivariate Legendre series. |
Polynomial1D (degree[, domain, window, …]) |
1D Polynomial model. |
Polynomial2D (degree[, x_domain, y_domain, …]) |
2D Polynomial model. |
SIP (crpix, a_order, b_order[, a_coeff, …]) |
Simple Imaging Polynomial (SIP) model. |
OrthoPolynomialBase (x_degree, y_degree[, …]) |
This is a base class for the 2D Chebyshev and Legendre models. |
PolynomialModel (degree[, n_models, …]) |
Base class for polynomial models. |
Class Inheritance Diagram¶
astropy.modeling.projections Module¶
Implements projections–particularly sky projections defined in WCS Paper II [R4aef2d5abf34-1].
All angles are set and and displayed in degrees but internally computations are performed in radians. All functions expect inputs and outputs degrees.
References¶
[R4aef2d5abf34-1] | Calabretta, M.R., Greisen, E.W., 2002, A&A, 395, 1077 (Paper II) |
Classes¶
Class Inheritance Diagram¶
astropy.modeling.rotations Module¶
Implements rotations, including spherical rotations as defined in WCS Paper II [R487dd78e661d-1]
RotateNative2Celestial
and RotateCelestial2Native
follow the convention in
WCS Paper II to rotate to/from a native sphere and the celestial sphere.
The implementation uses EulerAngleRotation
. The model parameters are
three angles: the longitude (lon
) and latitude (lat
) of the fiducial point
in the celestial system (CRVAL
keywords in FITS), and the longitude of the celestial
pole in the native system (lon_pole
). The Euler angles are lon+90
, 90-lat
and -(lon_pole-90)
.
References¶
[R487dd78e661d-1] | Calabretta, M.R., Greisen, E.W., 2002, A&A, 395, 1077 (Paper II) |
Classes¶
RotateCelestial2Native (lon, lat, lon_pole, …) |
Transform from Celestial to Native Spherical Coordinates. |
RotateNative2Celestial (lon, lat, lon_pole, …) |
Transform from Native to Celestial Spherical Coordinates. |
Rotation2D ([angle]) |
Perform a 2D rotation given an angle. |
EulerAngleRotation (phi, theta, psi, …) |
Implements Euler angle intrinsic rotations. |
Class Inheritance Diagram¶
astropy.modeling.tabular Module¶
Tabular models.
Tabular models of any dimension can be created using tabular_model
.
For convenience Tabular1D
and Tabular2D
are provided.
Examples¶
>>> table = np.array([[ 3., 0., 0.],
... [ 0., 2., 0.],
... [ 0., 0., 0.]])
>>> points = ([1, 2, 3], [1, 2, 3])
>>> t2 = Tabular2D(points, lookup_table=table, bounds_error=False,
... fill_value=None, method='nearest')
Functions¶
tabular_model (dim[, name]) |
Make a Tabular model where n_inputs is based on the dimension of the lookup_table. |
-
class
astropy.modeling.tabular.
Tabular1D
(points=None, lookup_table=None, method='linear', bounds_error=True, fill_value=nan, **kwargs)¶ Tabular model in 1D. Returns an interpolated lookup table value.
Parameters: - points : array-like of float of ndim=1.
The points defining the regular grid in n dimensions.
- lookup_table : array-like, of ndim=1.
The data in one dimensions.
- method : str, optional
The method of interpolation to perform. Supported are “linear” and “nearest”, and “splinef2d”. “splinef2d” is only supported for 2-dimensional data. Default is “linear”.
- bounds_error : bool, optional
If True, when interpolated values are requested outside of the domain of the input data, a ValueError is raised. If False, then
fill_value
is used.- fill_value : float, optional
If provided, the value to use for points outside of the interpolation domain. If None, values outside the domain are extrapolated. Extrapolation is not supported by method “splinef2d”.
Returns: - value : ndarray
Interpolated values at input coordinates.
Raises: - ImportError
Scipy is not installed.
Notes
-
class
astropy.modeling.tabular.
Tabular2D
(points=None, lookup_table=None, method='linear', bounds_error=True, fill_value=nan, **kwargs)¶ Tabular model in 2D. Returns an interpolated lookup table value.
Parameters: - points : tuple of ndarray of float, with shapes (m1, m2), optional
The points defining the regular grid in n dimensions.
- lookup_table : array-like, shape (m1, m2)
The data on a regular grid in 2 dimensions.
- method : str, optional
The method of interpolation to perform. Supported are “linear” and “nearest”, and “splinef2d”. “splinef2d” is only supported for 2-dimensional data. Default is “linear”.
- bounds_error : bool, optional
If True, when interpolated values are requested outside of the domain of the input data, a ValueError is raised. If False, then
fill_value
is used.- fill_value : float, optional
If provided, the value to use for points outside of the interpolation domain. If None, values outside the domain are extrapolated. Extrapolation is not supported by method “splinef2d”.
Returns: - value : ndarray
Interpolated values at input coordinates.
Raises: - ImportError
Scipy is not installed.
Notes
astropy.modeling.mappings Module¶
Special models useful for complex compound models where control is needed over which outputs from a source model are mapped to which inputs of a target model.
Classes¶
Mapping (mapping[, n_inputs, name, meta]) |
Allows inputs to be reordered, duplicated or dropped. |
Identity (n_inputs[, name, meta]) |
Returns inputs unchanged. |
Class Inheritance Diagram¶
astropy.modeling.fitting Module¶
This module implements classes (called Fitters) which combine optimization
algorithms (typically from scipy.optimize
) with statistic functions to perform
fitting. Fitters are implemented as callable classes. In addition to the data
to fit, the __call__
method takes an instance of
FittableModel
as input, and returns a copy of the
model with its parameters determined by the optimizer.
Optimization algorithms, called “optimizers” are implemented in
optimizers
and statistic functions are in
statistic
. The goal is to provide an easy to extend
framework and allow users to easily create new fitters by combining statistics
with optimizers.
There are two exceptions to the above scheme.
LinearLSQFitter
uses Numpy’s lstsq
function. LevMarLSQFitter
uses
leastsq
which combines optimization and statistic in one
implementation.
Classes¶
LinearLSQFitter () |
A class performing a linear least square fitting. |
LevMarLSQFitter () |
Levenberg-Marquardt algorithm and least squares statistic. |
FittingWithOutlierRemoval (fitter, outlier_func) |
This class combines an outlier removal technique with a fitting procedure. |
SLSQPLSQFitter () |
SLSQP optimization algorithm and least squares statistic. |
SimplexLSQFitter () |
Simplex algorithm and least squares statistic. |
JointFitter (models, jointparameters, initvals) |
Fit models which share a parameter. |
Fitter (optimizer, statistic) |
Base class for all fitters. |
Class Inheritance Diagram¶
astropy.modeling.optimizers Module¶
Optimization algorithms used in fitting
.
Classes¶
Optimization (opt_method) |
Base class for optimizers. |
SLSQP () |
Sequential Least Squares Programming optimization algorithm. |
Simplex () |
Neald-Mead (downhill simplex) algorithm. |
Class Inheritance Diagram¶
astropy.modeling.statistic Module¶
Statistic functions used in fitting
.
Functions¶
leastsquare (measured_vals, updated_model, …) |
Least square statistic with optional weights. |
astropy.modeling.separable Module¶
Functions to determine if a model is separable, i.e. if the model outputs are independent.
It analyzes n_inputs
, n_outputs
and the operators
in a compound model by stepping through the transforms
and creating a coord_matrix
of shape (n_outputs
, n_inputs
).
Each modeling operator is represented by a function which
takes two simple models (or two coord_matrix
arrays) and
returns an array of shape (n_outputs
, n_inputs
).
Functions¶
is_separable (transform) |
A separability test for the outputs of a transform. |
separability_matrix (transform) |
Compute the correlation between outputs and inputs. |