[R] vector decreasing by a factor

[(Ted Harding)]

On 02-May-11 07:55:27, andre bedon wrote:
> Hi,
> I'm quite new to R so this question will sound quite fundamental.
> I need to create a vector of length 160. The first element should
> be (1+r)^159 and each element thereafter should decrease by a
> factor of (1+r) until the 160th element that should be 1.
> Is there a function similar to seq() but increasing or decreasing
> by factors? I need to do this in one step i.e, not using loops.
> Any help would be greatly appreciated. 
> Regards,
> Andre

One expression which would do what you want is

  rev((1+r)^(0:159))

though there may be more efficient ways to do it. This assumes
that r, hence (1+r), is given. If you are given the
value X1 of the first element, which is to be interpreted
as (1+r)^159, then perhaps take (1+r) as X1^(1/159),
though there is a potential slight inaccuracy in recovering
X0 from (1+r)^159. So check this first.

Hoping this helps,
Ted.

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Date: 02-May-11                                       Time: 09:50:55
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