I wouldn't know of any valid output when applying the sign function to NaN. Therefore, I think it is correct to return a ValueError. Furthermore, I would prefer such an error over just returning NaN since it helps you locating where NaN is generated.

On Tue, Sep 29, 2015 at 5:13 PM, Charles R Harris <charlesr.harris@gmail.com> wrote:
Hi All,

Due to a recent commit, Numpy master now raises an error when applying the sign function to an object array containing NaN. Other options may be preferable, returning NaN for instance, so I would like to open the topic for discussion on the list.

Thoughts?

Chuck

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