function S=maternos(k,s2,nu,rho)
% S=MATERNOS(k,s2,nu,rho)
%
% Calculates the three-parameter Matern spectral density used by 
% Olhede & Simons 
%
% INPUT:
%
% k        Wavenumber(s), e.g. from KNUM2 [rad/m] - unwrapped 
% s2       The first Matern parameter, aka sigma^2
% nu       The second Matern parameter
% rho      The third Matern parameter
%
% OUTPUT:
%
% S        A column vector with all the wavenumbers unwrapped
%
% Last modified by fjsimons-at-alum.mit.edu, 02/29/2012

avark=4*nu/pi^2/rho^2+k(:).^2;
S=s2*nu^(nu+1)*4^nu/pi/(pi*rho)^(2*nu).*avark.^(-nu-1);