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

NumPy Trac numpy-tickets@scipy....
Tue Sep 7 16:39:26 CDT 2010

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

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>
NumPy <http://projects.scipy.org/numpy>
My example project
```

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