Re: Suggestion: math.between()
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- Subject: Re: Suggestion: math.between()
- From: Kristofer Karlsson <kristofer.karlsson@...>
- Date: 2010年6月22日 07:56:56 +0200
Wow, for such a seemingly simple function, a lot of people have come up with either really strange implementations or simple but wrong ones.
I like Jeffs and Davids versions though!
Here's a tail recursive version:
local function meanworker(mean, index, x, ...)
if x then
return meanworker(mean + (x - mean) / index, index + 1, ...)
end
return mean
end
function mean(...)
return meanworker(0, 1, ...)
end
On Tue, Jun 22, 2010 at 3:14 AM, David Manura
<dm.lua@math2.org> wrote:
On Mon, Jun 21, 2010 at 8:30 PM, Jonathan Castello <
twisolar@gmail.com> wrote:
> It's really just the average of two numbers, (x+y)/2. An averaging
> function isn't such a bad idea, particularly if it takes an arbitrary
> number of parameters (like Jeff Pohlmeyer's implementation in this
> thread).
in Python's math.fsum [1] and [2].
This version of mean is less efficient but supports incremental
computation and is less prone to overflow (not that overflow would
likely happen for floating point numbers):
local function mean(...)
local mean = 0
for i=1,select('#', ...) do
mean = mean + (select(i, ...) - mean) / i
end
return mean
end
[1] http://docs.python.org/library/math.html#math.fsum
[2] http://en.wikipedia.org/wiki/Compensated_summation