[Numpy-discussion] numpy dot returns [nan nan nan]

[Warren Weckesser]

On 8/24/13, Tom Bennett <tom.bennett at mail.zyzhu.net> wrote:
> Hi All,
>
> I have two arrays, A and B.A is 3 x 100,000 and B is 100,000. If I do
> np.dot(A,B), I get [nan, nan, nan].
>
> However, np.any(np.isnan(A))==False and np.any(no.isnan(B))==False. And
> also np.seterr(all='print') does not print anything.
>
> I am not wondering what is going on and how to avoid.
>
> In case it is important, A and B are from the normal equation of doing
> regression. I am regressing 100,000 observations on 3 100,000 long factors.
>
> Thanks,
> Tom
>

What are the data types of the arrays, and what are the typical sizes
of the values in these arrays?  I can get all nans from np.dot if the
values are huge floating point values:

```
In [79]: x = 1e160*np.random.randn(3, 10)

In [80]: y = 1e160*np.random.randn(10)

In [81]: np.dot(x, y)
Out[81]: array([ nan,  nan,  nan])
```

Warren