function dxzdt = pp1(t,xz)
% PP1 of the
%      
%   See also 
%   Matthhias Kawski, June 2005

global KX;
global KZ;
global NL;

dxzdt = [0 -1 -KX 0; 1 0 0 0; 0 0 -KX -1;0 1 1 -KZ]*xz+...
        NL*xz(1)*xz(2)*[-1 1 0 0]';