[rrd-developers] Unexpected behaviour of PREDICT and PREDICTSIGMA

Steve Shipway s.shipway at auckland.ac.nz
Wed Apr 23 23:52:44 CEST 2014

So, I'm delving into the PREDICT operations in the RPN, and have found
something unexpected.


There are two ways of specifying the shift offsets - as a (positive) count
of shifts and a list; or as a negative count and a base shift.





My tests (using 1.4.trunk) indicate that the two above have identical
behaviour.  My question is, is this intended?  In particular, when giving a
negative  shift count, should the resulting list of shifts be based at 0?  


Given this:




I had expected to get shifts of s, 2s and 3s.  Instead I get 0, s and 2s.
Is this intentional, or a feature?


As a corollary, it means that these two lines are also equal for ANY value
of s










Steve Shipway

University of Auckland

UNIX Systems Design Team Lead

s.shipway at auckland.ac.nz

+64 (9) 3737 599 ext 86487


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