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+## Copyright (C) 2000 Paul Kienzle
+##
+## This file is part of Octave.
+##
+## Octave is free software; you can redistribute it and/or modify it
+## under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 2, or (at your option)
+## any later version.
+##
+## Octave is distributed in the hope that it will be useful, but
+## WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+## General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with Octave; see the file COPYING.  If not, write to the Free
+## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+## 02110-1301, USA.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{pp} = } mkpp (@var{x}, @var{p})
+## @deftypefnx {Function File} {@var{pp} = } mkpp (@var{x}, @var{p}, @var{d})
+## 
+## Construct a piece-wise polynomial structure from sample points
+## @var{x} and coefficients @var{p}.  The ith row of @var{p},
+## @code{@var{p} (@var{i},:)}, contains the coefficients for the polynomial
+## over the @var{i}-th interval, ordered from highest to 
+## lowest. There must be one row for each interval in @var{x}, so 
+## @code{rows (@var{p}) == length (@var{x}) - 1}.  
+##
+## You can concatenate multiple polynomials of the same order over the 
+## same set of intervals using @code{@var{p} = [ @var{p1}; @var{p2}; 
+## @dots{}; @var{pd} ]}.  In this case, @code{rows (@var{p}) == @var{d} 
+## * (length (@var{x}) - 1)}.
+##
+## @var{d} specifies the shape of the matrix @var{p} for all except the
+## last dimension. If @var{d} is not specified it will be computed as
+## @code{round (rows (@var{p}) / (length (@var{x}) - 1)) instead.
+##
+## @seealso{unmkpp, ppval, spline}
+## @end deftypefn
+
+function pp = mkpp (x, P, d)
+  if (nargin < 2 || nargin > 3)
+    usage ("pp = mkpp(x,P,d)");
+  endif
+  pp.x = x(:);
+  pp.P = P;
+  pp.n = length (x) - 1;
+  pp.k = columns (P);
+  if (nargin < 3)
+    d = round (rows (P) / pp.n); 
+  endif
+  pp.d = d;
+  if (pp.n*d != rows (P))
+    error ("mkpp: num intervals in x doesn't match num polynomials in P");
+  endif
+endfunction
+
+%!demo # linear interpolation
+%! x=linspace(0,pi,5)'; 
+%! t=[sin(x),cos(x)];
+%! m=diff(t)./(x(2)-x(1)); 
+%! b=t(1:4,:);
+%! pp = mkpp(x, [m(:),b(:)]);
+%! xi=linspace(0,pi,50);
+%! plot(x,t,"x;control;",xi,ppval(pp,xi),";interp;");