%
%  contour plot example -- lect01a.m
%     - to run, type "lect01a" at the matlab prompt
%
%     - to get browser help, access "helpdesk"
%       from the menu of any plot!
%     - to get in-line help for a command "xyz", 
%       type "help xyz" at the matlab prompt
%
%- - - - - - - - - - - - - - - - - - - - - - - - 

a = 1.2;   b = 0.5;

u = -2:0.01:2;   up = u;

%  matrices of values

[u1 u2] = meshgrid(u,up);
k = 0.5*(u2.^2)  - ((b/4)*(u1.^4) - (a/2)*(u1.^2));

%  contourplot

hpi = pi/2;
co = - ((b/4)*(hpi^4) - (a/2)*(hpi^2));
cont = [0:co/5:4*co];
contour(u,up,k,cont)

title('\bf phase plane')
xlabel('\bf u')
ylabel('\bf u \prime')