Re: periodic cspline first derivative discontinuity

[Brian Gough <bjg at network-theory dot co dot uk>]

David Necas (Yeti) writes:
 >  I've found a bug (or I think I've found a bug ;-) in periodic
 > cubic spline implementation -- its first derivative is not
 > continuous at the edges of the first segment.
 >  This is because length of next segment (h_ip1 in the patch below)
 > is computed modulo even for the last segment and so it results as
 > negative (well, not much clearly explained, perhaps the patch
 > itself is clearer).
 >  Please note applying this patch actually fixes only first
 > derivative discontinuity in right edge of the first segment, some
 > dicontinuity may still appear at the left edge due to probems in
 > cyclic tridiagonal linear system solver -- see my next bugreport.

Can you tell me how the patch to fix the cyclic solver affects this
result? Is any further change needed to the spline code?  
Thanks 
Brian