Google Groups no longer supports new Usenet posts or subscriptions. Historical content remains viewable.
Dismiss

Power equation

17 views
Skip to first unread message

Diogo Alves

unread,
Apr 26, 2012, 11:47:43 AM4/26/12
to
In the following equation:

c = sum_i( ( p(i)^a ) * b(i) ) / sum_i( p(i)^a )

"c", "p(i)" and "b(i)" are known.
How do I calculate "a"?
Message has been deleted

Rick Decker

unread,
Apr 26, 2012, 11:53:17 AM4/26/12
to
You can't, in general. Suppose, for example you
had p(i) = 1 for all i.


Regards,

Rick

Diogo Alves

unread,
Apr 26, 2012, 12:04:14 PM4/26/12
to
Not even knowing that " 0 <= p(i) < 1" ?

Dave

unread,
Apr 26, 2012, 1:22:28 PM4/26/12
to
Write
f(x) = sum_i( ( p(i)^x ) * b(i) ) / sum_i( p(i)^x ) - c
and use a numeric technique such as Newton's Method to solve the equation f(x) = 0.

Dave

Diogo Alves

unread,
Apr 26, 2012, 5:58:36 PM4/26/12
to
I was really hoping for an analytic solution but thank you very much for your suggestion.
0 new messages