Numbers in Geometric Progression

问题

How can i generate a sequence of numbers which are in Geometric Progression in R? for example i need to generate the sequence : 1, 2,4,8,16,32 and so on....till say a finite value?

回答1:

Here's what I'd do:

geomSeries <- function(base, max) {
    base^(0:floor(log(max, base)))
}

geomSeries(base=2, max=2000)
# [1]    1    2    4    8   16   32   64  128  256  512 1024

geomSeries(3, 100)
# [1]  1  3  9 27 81

回答2:

Why not just enter 2^(0:n)? E.g. 2^(0:5) gets you from 1 to 32 and so on. Capture the vector by assigning to a variable like so: x <- 2^(0:5)

回答3:

You can find any term in a geometric sequence with this mathematical function:

term = start * ratio ** (n-1)

Where:

term = the term in the sequence that you want
start = the first term in the sequence
ratio = the common ratio (i.e. the multiple that defines the sequence)
n = the number of the term in the sequence that you want

Using this information, write up a function in R that provides any subset of a geometric sequence for any start and ratio:

#begin = beginning of subset
#end = end of subset

geomSeq <- function(start,ratio,begin,end){
  begin=begin-1
  end=end-1
  start*ratio**(begin:end)
}

geomSeq(1, 2, 1, 10)
# [1]   1   2   4   8  16  32  64 128 256 512

geomSeq(10,3,1,8)
# [1]    10    30    90   270   810  2430  7290 21870

geomSeq(10,3,4,8)
# [1]   270   810  2430  7290 21870