function s = sph(x,D)

%SPHER = spherical variogram.

%INPUTS: (i)   x(1) = range
%        (ii)  x(2) = sill
%        (iii) x(3) = nugget
%        (iii) D = (m,1) vector of dist values (di)
%OUTPUT:
%        s = (m,1) vector of spherical values for D

m = length(D) ;

s = zeros(m,1) ;

D = min(D,x(1)*ones(m,1)) ;
     
s = (x(3)*ones(m,1)) + (x(2) - x(3)) *...
          (((3*D)/(2*x(1))) - ((D.^3)/(2*x(1)^3)));