ANSI C code from the article
"Smoothing and Interpolation with Finite Differences"
by Paul H. C. Eilers, paul@dcmr.nl
in "Graphics Gems IV", Academic Press, 1994

files:
    smooth1.c: Smoothing and interpolation with first differences.
    smooth2.c: Smoothing and interpolation with second differences.
    smooth3.c: Smoothing and interpolation with any difference equation.
