% trigfield2A.m turns an evolving trig field into a movie

gridsize = [40 40];
[x,y]    = easygrid([0 15 0 15], gridsize);     % [xmin xmax ymin ymax]
clear Zm

m        = 10;                                  % number of modes

A        = randn(1,m)*sqrt(2/m);                % amplitudes of Fourier modes
phi      = 2 * pi * rand(m,1);                  % random phase
norm     = sqrt(-2*log(rand(m,1)));             % magnitudes of wave numbers
theta    = 2 * pi * rand(m,1);                  % arguments of wave numbers
K        = [norm.*cos(theta) norm.*sin(theta)]; % isotropic wave numbers

for C=1:30,

for i=1:gridsize(1),                            % step through grid points
 for j=1:gridsize(2),
  Zm(i,j,1,C) = A * cos(K*[x(i,j); y(i,j)] + phi); % compute field value at x,y
 end
end

A = cos(.1)*A + sin(.1)*randn(1,m)*sqrt(2/m);     
                                       % small change in A; variances sum to 1
end

mi  = min(min(min(Zm)));
ma  = max(max(max(Zm)));
Zm   = (Zm-mi)*length(jet)/(ma-mi);      % scale Z values to run from 0 to 
                                         % number of rows in the colormap jet

clf

mov = immovie(Zm,jet);           % paste Zm values into a movie

movie(mov,3);                    % cycle through the movie 3 times