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_fx_nmda.m
    path of file: ./repos/spm/toolbox/dcm_meeg
    
    the code of the file until where you have to start completion: function [f,J,Q] = spm_fx_nmda(x,u,P,M)
% State equations for neural-mass and mean-field models
% FORMAT [f,J,Q] = spm_fx_nmda(x,u,P,M)
%
% x - states and covariances
%
% x{1}(i,j,k)   - k-th state of j-th population of i-th source
%                 i.e., running over sources, pop. and states
% x{2}(:,:,i,j) - covariance among k states
%                 i.e., running over states x states, sources and pop.
%
%   population: 1 - excitatory spiny stellate cells (input cells)
%               2 - inhibitory interneurons
%               3 - excitatory pyramidal cells      (output cells)
%
%        state: 1 V  - voltage
%               2 gE - conductance (excitatory)
%               3 gI - conductance (inhibitory)
%
%--------------------------------------------------------------------------
% refs:
%
% Marreiros et al (2008) Population dynamics under the Laplace assumption
%
% See also:
%
% Friston KJ.

    
function [f,J,Q] = spm_fx_nmda(x,u,P,M)
% State equations for neural-mass and mean-field models
% FORMAT [f,J,Q] = spm_fx_nmda(x,u,P,M)
%
% x - states and covariances
%
% x{1}(i,j,k)   - k-th state of j-th population of i-th source
%                 i.e., running over sources, pop. and states
% x{2}(:,:,i,j) - covariance among k states
%                 i.e., running over states x states, sources and pop.
%
%   population: 1 - excitatory spiny stellate cells (input cells)
%               2 - inhibitory interneurons
%               3 - excitatory pyramidal cells      (output cells)
%
%        state: 1 V  - voltage
%               2 gE - conductance (excitatory)
%               3 gI - conductance (inhibitory)
%
%--------------------------------------------------------------------------
% refs:
%
% Marreiros et al (2008) Population dynamics under the Laplace assumption
%
% See also:
%
% Friston KJ.
% The labile brain. I. Neuronal transients and nonlinear coupling. Philos
% Trans R Soc Lond B Biol Sci. 2000 Feb 29;355(1394):215-36. 
% 
% McCormick DA, Connors BW, Lighthall JW, Prince DA.
% Comparative electrophysiology of pyramidal and sparsely spiny stellate
% neurons of the neocortex. J Neurophysiol. 1985 Oct;54(4):782-806.
% 
% Brunel N, Wang XJ.
% What determines the frequency of fast network oscillations with irregular
% neural discharges? I. Synaptic dynamics and excitation-inhibition
% balance. J Neurophysiol. 2003 Jul;90(1):415-30.
% 
% Brunel N, Wang XJ.
% Effects of neuromodulation in a cortical network model of object working
% memory dominated by recurrent inhibition. J Comput Neurosci. 2001
% Jul-Aug;11(1):63-85.
%
%__________________________________________________________________________
 
% Karl Friston
% Copyright (C) 2005-2022 Wellcome Centre for Human Neuroimaging

 
% get dimensions and configure state variables
%--------------------------------------------------------------------------
try, x = spm_unvec(x,M.x); end