[AstroPy] astropy.modeling.fitting Using Weights in 2d Fits

[Nathan De Lee]

Hi Everyone,

I am trying to fit a 2d Gaussian with weights for each data point using 
the astropy.modeling.fitting in astropy version 1.3. When I try this 
using a 1d Gaussian model everything seems to work fine, but I am 
encountering a shape error when I try to do it in the 2d case. The 
weights have the same shape (21,21) as everything else. The code I used 
and the error is below. Am I doing something wrong, or is there a bug 
that I am running into?

Thanks for any help you can give,

Nathan

Code:

from astropy.modeling import models,fitting
import numpy as np

def gaussian(height, center_x, center_y, width_x, width_y):
     """Returns a gaussian function with the given parameters"""
     width_x = float(width_x)
     width_y = float(width_y)
     return lambda x,y: height*np.exp(
-(((center_x-x)/width_x)**2+((center_y-y)/width_y)**2)/2)

Xin, Yin = np.mgrid[0:21, 0:21]
y = gaussian(10, 10, 9, 2, 3)(Xin, Yin)

#Add gaussian noise to the function with a random sigma between 0.1 and 1.1
ysig = 1*np.random.rand(Xin.shape[0],Xin.shape[1]) + 0.1
y = y + np.random.normal(0., ysig, Xin.shape)
#Fit the data
gauss2d_init = models.Gaussian2D(amplitude=15, x_mean=5, y_mean=5, 
x_stddev=1, y_stddev=1, theta=0)
fit_gauss2d = fitting.LevMarLSQFitter()
gmod = fit_gauss2d(gauss2d_init, Xin, Yin, y,weights=1.0/ysig)

Error:

---------------------------------------------------------------------------
ValueError                                 Traceback (most recent call last)
<ipython-input-8-589f3eb378b7>  in<module>() 12 print(y.shape)13 fit_gauss2d = 
fitting.LevMarLSQFitter()---> 14gmod = fit_gauss2d(gauss2d_init, Xin, 
Yin, y,weights=1.0/ysig)15 print(fit_gauss2d.fit_info.keys())16 
print("{} {} {} {} {} 
{}".format(*gmod.param_names))/home/deleenm/anaconda2/lib/python2.7/site-packages/astropy/modeling/fitting.pyc 
in __call__(self, model, x, y, z, weights, maxiter, acc, epsilon, 
estimate_jacobian) 558 self.objective_function, init_values, args=farg, 
Dfun=dfunc,559 col_deriv=model_copy.col_fit_deriv, maxfev=maxiter, 
epsfcn=epsilon,--> 560xtol=acc, full_output=True) 561 
_fitter_to_model_params(model_copy, fitparams)562 
self.fit_info.update(dinfo)/home/deleenm/anaconda2/lib/python2.7/site-packages/scipy/optimize/minpack.pyc 
in leastsq(func, x0, args, Dfun, full_output, col_deriv, ftol, xtol, 
gtol, maxfev, epsfcn, factor, diag) 388 else:389 if col_deriv:--> 
390_check_func('leastsq', 'Dfun', Dfun, x0, args, n, (n, m))391 else:392 
_check_func('leastsq', 'Dfun', Dfun, x0, args, n, (m, 
n))/home/deleenm/anaconda2/lib/python2.7/site-packages/scipy/optimize/minpack.pyc 
in _check_func(checker, argname, thefunc, x0, args, numinputs, 
output_shape) 24 def _check_func(checker, argname, thefunc, x0, args, 
numinputs, 25 output_shape=None): ---> 26res = 
atleast_1d(thefunc(*((x0[:numinputs],) + args)))27 if (output_shape is 
not None) and (shape(res) != output_shape):28 if (output_shape[0] != 
1):/home/deleenm/anaconda2/lib/python2.7/site-packages/astropy/modeling/fitting.pyc 
in _wrap_deriv(params, model, weights, x, y, z) 620 return [np.ravel(_) 
for _ in np.ravel(weights) * np.array(model.fit_deriv(x, *params))]621 
else:--> 622return [np.ravel(_) for _ in (np.ravel(weights) * 
np.array(model.fit_deriv(x, y, *params)).T).T]623 624 ValueError: 
operands could not be broadcast together with shapes (441,) (21,21,6)

-- 
Dr. Nathan De Lee
Assistant Professor of Astronomy and Physics
Northern Kentucky University
151 Science Center
1 Nunn Drive
Highland Heights, KY 41099
Tel: 859-572-5492
Fax: 859-572-6092
www.nku.edu/~deleen1
deleenm at nku.edu

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