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 statements to pin-point its origin.

```
Warning: invalid value encountered in double_scalars
Warning: invalid value encountered in double_scalars
Warning: invalid value encountered in double_scalars
Warning: invalid value encountered in double_scalars

```

Is this is a Numpy warning, and what is a double scalar?

From Numpy I use

```
min(), argmin(), mean() and random.randn()

```

I also use Matplotlib

Answer: 
In my case, I found out it was division by zero.
Whenever you are working with csv imports, try to use df.dropna() to avoid all such warnings or errors.