'invalid value encountered in double_scalars' warning, possibly numpy

Question

As I run my code I get these warnings, always in groups of four, sporadically. I have tried to locate the source by placing debug messages before and after certain statement

Answer 1

Zero-size array passed to numpy.mean raises this warning (as indicated in several comments).

For some other candidates:

• median also raises this warning on zero-sized array.

other candidates do not raise this warning:

• min,argmin both raise ValueError on empty array
• randn takes *arg; using randn(*[]) returns a single random number
• std,var return nan on an empty array