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# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""
Statistic functions used in `~astropy.modeling.fitting`.
"""
from __future__ import (absolute_import, unicode_literals, division,
print_function)
import numpy as np
__all__ = ['leastsquare']
def leastsquare(measured_vals, updated_model, weights, x, y=None):
"""
Least square statistic with optional weights.
Parameters
----------
measured_vals : `~numpy.ndarray`
Measured data values.
updated_model : `~astropy.modeling.Model`
Model with parameters set by the current iteration of the optimizer.
weights : `~numpy.ndarray`
Array of weights to apply to each residual.
x : `~numpy.ndarray`
Independent variable "x" to evaluate the model on.
y : `~numpy.ndarray`, optional
Independent variable "y" to evaluate the model on, for 2D models.
Returns
-------
res : float
The sum of least squares.
"""
if y is None:
model_vals = updated_model(x)
else:
model_vals = updated_model(x, y)
if weights is None:
return np.sum((model_vals - measured_vals) ** 2)
else:
return np.sum((weights * (model_vals - measured_vals)) ** 2)
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