[NumPy-Tickets] [NumPy] #1606: broadcasting masked arrays in exponents

[NumPy Trac]

#1606: broadcasting masked arrays in exponents
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 Reporter:  weathergod  |       Owner:  pierregm
     Type:  defect      |      Status:  new     
 Priority:  normal      |   Milestone:  2.0.0   
Component:  numpy.ma    |     Version:  1.5.0   
 Keywords:              |  
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Comment(by weathergod):

 I should have used the Preview button... corrected version below.

 {{{
 import numpy as np

 a_2d = np.random.random((3, 5))
 b_1d = np.random.random(5)
 b_2d = np.vstack((b_1d, b_1d, b_1d))

 a_ma_2d = np.ma.masked_array(a_2d, mask=(numpy.random.random((3, 5)) <
 0.25))
 b_ma_1d = np.ma.masked_array(b_1d, mask=(numpy.random.random(5) < 0.25))
 b_ma_2d = np.ma.masked_array(b_2d, mask=(numpy.random.random((3, 5)) <
 0.25))

 # a**b                    without broadcasting (works)
 print a_2d**b_2d

 # a**b                    with broadcasting (works)
 print a_2d**b_1d

 # a_ma**b_ma     without broadcasting (works)
 print a_ma_2d**b_ma_2d

 # a_ma**b_ma     with broadcasting (works)
 print a_ma_2d**b_ma_1d

 # a**b_ma            without broadcasting (works)
 print a_2d**b_ma_2d

 # a**b_ma            with broadcasting (FAILS)
 print a_2d**b_ma_1d
 Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "/home/bvr/Programs/numpy/numpy/ma/core.py", line 3697, in __rpow__
     return power(other, self)
   File "/home/bvr/Programs/numpy/numpy/ma/core.py", line 6043, in power
     m |= invalid
 ValueError: invalid return array shape

 # Now, test broadcasting of the other side of the operator
 c = np.random.random(5)
 c_ma = np.ma.masked_array(c, mask=(np.random.random(10) < 0.25))

 # c**b_ma                with broadcasting (works)
 print c**b_ma_2d

 # c_ma**b                with broadcasting (FAILS)
 print c_ma**b_2d
 Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "/home/bvr/Programs/numpy/numpy/ma/core.py", line 3693, in __pow__
     return power(self, other)
   File "/home/bvr/Programs/numpy/numpy/ma/core.py", line 6043, in power
     m |= invalid
 ValueError: invalid return array shape
 }}}

 So, this fails if we broadcast the masked array portion of a power
 expression and the other value is a ndarray.
 Note, the same also occurs if we broadcast a masked array in order to
 raise it to powers indicated by an ndarray.

-- 
Ticket URL: <http://projects.scipy.org/numpy/ticket/1606#comment:1>
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