% Subroutine used to construct and evaluate the spline 
% once the coefficients aj's, ... dj's have been computed.
% It can be applied to both free or natural or clamped boundaries.

function [vp]=splp(x,a,b,c,d,p,N)
for i=1:N-1
   if p>=x(i) & p<x(i+1), 
      vp=a(i)+b(i).*(p-x(i))+c(i).*(p-x(i)).^2+d(i)*(p-x(i)).^3; break, 
   end;
   if p>=x(N), 
      vp=a(N-1)+b(N-1).*(p-x(N-1))+c(N-1).*(p-x(N-1)).^2+d(N-1)*(p-x(N-1)).^3; break, 
   end; 
end