Re: Some way to differentiate (1st order derivative)?

[Ethan M. <merritt@u.washington.edu>]

On Wednesday 24 October 2007 05:45, pl...@pi... wrote:
> 
> if you want to post that as an example it should probably by plotting  
> against ($1+old_x)/2 to prevent a shift in the position of the derivative.
> 
> BTW the running mean example also suffers from this defect as is clearly  
> seen in the plot that Ethan linked to. The running mean is offset 2.5 data  
> points to the right.

The running mean example is correct for the typical use case.
Have a look in your local paper for the stock price reports,
or the weather summaries, etc.

In calculating a running average you typically do not known the value of
future points, only of the points measured to date.
So you necessarily average over the previous 5 points, as stated in the
plot title.  

This is not the same as for local approximation of the derivative.

-- 
Ethan A Merritt