Sqrt of a negative value return zero instead of NaN #3852

Hi, I found that sqrt function in cntk returns 0 instead of NaN for negative numbers, which is different from other deep learning libraries, such as tensorflow and theano. I'm not sure if this is a bug?

>>> import cntk as C
>>> C.sqrt(-1).eval()
array(0., dtype=float32)
>>> C.sqrt(-2).eval()
array(0., dtype=float32)
>>> C.sqrt(-4).eval()
array(0., dtype=float32)

Windows 10 x64, cntk 2.7.0, CPU only.