[Numpy-discussion] Precision/value change moving from C to Python

[Daπid]

On 12 November 2013 12:01, Bart Baker <bartbkr at gmail.com> wrote:

> The issue is that there are some minor (10^-16) differences in the
> values when I do the calculation in C vs Python.
>

That is the order of the machine epsilon for double, that looks like
roundoff errors to me.

 I found similar results cythonising some code, everything was the same
until I changed some numpy functions for libc functions (exp, sin, cos...).
After some operations in float32, the results were apart for 1 in 10^-5
(the epsilon is 10^-6). I blame them on specific implementation differences
between numpy's and my system's libc specific functions.

To check equality, use np.allclose, it lets you define the relative and
absolute error.


/David.
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