xidulu commented on issue #16460: numpy -> mxnet -> numpy gives arrays with 
strange behavior 
URL: 
https://github.com/apache/incubator-mxnet/issues/16460#issuecomment-541427480
 
 
   Hi @vafl 
   
   I did the following experiment:
   
   ```
   In [1]: import numpy as np
   
   In [2]: n = 1_000_000
   
   In [3]: x = np.array([100.0, -100.0])[None, :].repeat(repeats=n, axis=0)
   
   In [4]: x.dtype
   Out[4]: dtype('float64')
   
   In [5]: x.astype('float32').std(axis=0)
   Out[5]: array([1.3201232, 1.3201232], dtype=float32)
   
   In [6]: import mxnet as mx
   
   In [7]: u = mx.nd.array(x)
   
   In [8]: u.dtype
   Out[8]: numpy.float32
   ```
   
   It seems that the root causes of your problem are: 1. The type conversion 
between Numpy.ndarray and mx.ndarray. 2. The numerical error from Numpy.
   
   I would suggest you could either raise this issue in Numpy's repo or 
manually declare the array's dtype using `.astype('float64')`.

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