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From Ted Dunning <ted.dunn...@gmail.com>
Subject Re: link() function in AbstractOnlineLogisticRegression class
Date Fri, 23 May 2014 12:48:47 GMT
exp(40) > 10^17

Thus, if x >= 1, for x + exp(-40) all significant bits of the exponential
are lost and the result is identical to just saying x.  Likewise for x <=1,
for 1+exp(40), the addition of 1 has no effect.

The logistic function [1] is defined as f(x) = 1 / (1 + exp(-x)), thus when
using double precision floating point where x >= 40, f(x) = 1 and where x
<= -40, f(x) = 0.


[1] https://en.wikipedia.org/wiki/Logistic_function



On Fri, May 23, 2014 at 4:23 AM, namit maheshwari <
namitmaheshwari7@gmail.com> wrote:

> Hello Everyone,
>
> In mahout's *AbstractOnlineLogisticRegression *class the *public static
> Vector link(Vector v)*
> function checks the *max* value against 40.
>
> Could anyone please explain the significance of 40 in context of Logistic
> Regression?
>
> Thanks
> Namit
>

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