function sph = spher(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:
%        sph = (m,1) vector of spherical values for D

m = length(D) ;

sph = zeros(m,1) ;

for i = 1:m
   
   if D(i) <= x(1)
      
      sph(i) = abs(x(3)) + (x(2) - abs(x(3))) *...
          (((3*D(i))/(2*x(1))) - ((D(i)^3)/(2*x(1)^3))); 
      
   else
      
      sph(i) = x(2) ;
      
   end
   
end