# HG changeset patch
# User Rik <rik@octave.org>
# Date 1544506899 28800
# Node ID 33e6ab3e14917f3c9bc0accffdea22f6b41775bb
# Parent  704cd93ca74898356ce13fe42e9451242da73d39
mkpp.m: Document how ppval will calculate values for each piecewise section (patch #9095).

* mkpp.m: Add Programming Note to documentation explaining how the lower bound
of the piecewise segment will be subtracted from the value of the polynomial
calculated for that segment.

diff -r 704cd93ca748 -r 33e6ab3e1491 scripts/polynomial/mkpp.m
--- a/scripts/polynomial/mkpp.m	Mon Dec 10 17:23:17 2018 -0800
+++ b/scripts/polynomial/mkpp.m	Mon Dec 10 21:41:39 2018 -0800
@@ -42,6 +42,10 @@
 ## @var{r}-th polynomial defined on interval @var{i}.  In any case @var{coefs}
 ## is reshaped to a 2-D matrix of size @code{[@var{ni}*prod(@var{d}) @var{m}]}.
 ##
+## Programming Note: @code{ppval} evaluates polynomials at
+## @code{@var{xi} - @var{breaks}(i)}, i.e., it subtracts the lower endpoint of
+## the current interval from @var{xi}.  This must be taken into account when
+## creating piecewise polynomials objects with @code{mkpp}.
 ## @seealso{unmkpp, ppval, spline, pchip, ppder, ppint, ppjumps}
 ## @end deftypefn