You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: spm_fp_display_nullclines.m
    path of file: ./repos/bspm/thirdparty/spm8
    
    the code of the file until where you have to start completion: function f = spm_fp_display_nullclines(M,x)
% Nullcline plot of flow and sample trajectory
% FORMAT spm_fp_display_nullclines(M,x)
%
% M   - model specifying flow; M(1).f;
% x   - cell array of domain or support
%
% f   - derivative of x(2)
%__________________________________________________________________________
% Copyright (C) 2005 Wellcome Trust Centre for Neuroimaging

% Karl Friston
% $Id: spm_fp_display_nullclines.m 2494 2008-11-26 20:08:15Z karl $

    
function f = spm_fp_display_nullclines(M,x)
% Nullcline plot of flow and sample trajectory
% FORMAT spm_fp_display_nullclines(M,x)
%
% M   - model specifying flow; M(1).f;
% x   - cell array of domain or support
%
% f   - derivative of x(2)
%__________________________________________________________________________
% Copyright (C) 2005 Wellcome Trust Centre for Neuroimaging

% Karl Friston
% $Id: spm_fp_display_nullclines.m 2494 2008-11-26 20:08:15Z karl $

% evaluation points and equilibria
%--------------------------------------------------------------------------
for i = 1:length(x)
    nx(i) = length(x{i});
end