Return the non-negative square-root of an array, element-wise.

// Examples
>>> np.sqrt([1,4,9])
array([ 1.,  2.,  3.])

>>> np.sqrt([4, -1, -3+4J])
array([ 2.+0.j,  0.+1.j,  1.+2.j])

>>> np.sqrt([4, -1, np.inf])
array([ 2., nan, inf])