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Re: st: Doing something an observation-specific number of times


From   Austin Nichols <austinnichols@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Doing something an observation-specific number of times
Date   Tue, 28 Aug 2012 13:23:11 -0400

robert hartman <rohartman@gmail.com>:
If you google "sum of finite geometric series" or somesuch, you should
find an easy answer.

On Tue, Aug 28, 2012 at 12:45 PM, robert hartman <rohartman@gmail.com> wrote:
> Hi Listers,
> Imagine that observation 1 has v1 and v2 values of .41 and 78,
> respectively. There are many other observations like this, where v1
> values lie on the unit interval and v2 values are positive integers
> (let's say the upper bounded is 600). I want to create a new variable
> and store in it the results of an algebraic equation that uses the v1
> and v2 values from same row, as well as some constants, and where
> "observation-specific exponentiation" is happening. For example, let's
> say I want to add a constant to v1 raised to some power and then
> divide that by some other constant. And let's say that the "some
> power" is  every power from 1 to the v2 value inclusive (e.g., 1
> through 78 in this case, 1 through 2 if the v2 value is 2...) and then
> sum up those terms.  For example, for observation 1, the new obs 1 v3
> value=((1+(.41^1))/2) + ((1+(.41^2))/2) ...((1+(.41^77))/2) +
> ((1+(.41^78))/2). The specific use case is convoluted, and I don't
> think in-depth understanding of it is critical to the programming
> (we'll see).
>
> I have begun to think of some klugy ways of doing this via looping or
> even the expand command. However, whereas my Stata programming skills
> are mediocre and have been acquired ad hoc, I thought some of you
> might have some insights as to a relatively computationally efficient
> and/or lines-of-code efficient way of doing this kind of thing. There
> may even be some kind of obvious (to you, not me) algebraic workaround
> that I'm not catching.
>
> Thanks,
> Rob
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