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_mmc.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_mmc(x,u,P,M)
% State equations for a neural mass model of motor cortex
% Bhatt et al. 2016 Neuroimage
%
% FORMAT [f,J,D] = spm_fx_mmc(x,u,P,M)
% FORMAT [f,J]   = spm_fx_mmc(x,u,P,M)
% FORMAT [f]     = spm_fx_mmc(x,u,P,M)
% x      - state vector
%   x(:,1) - voltage     (middle pyramidal cells)
%   x(:,2) - conductance (middle pyramdidal cells)
%   x(:,3) - voltage     (superficial pyramidal cells)
%   x(:,4) - conductance (sup
    
function
B    = 0;                        % bias or background (sigmoid)
R    = R.*exp(P.S);              % gain of activation function
F    = 1./(1 + exp(-R*x + B));   % firing rate
S    = F - 1/(1 + exp(B));       % deviation from baseline firing

% input
%==========================================================================
if isfield(M,'u')
    
    % endogenous input
    %----------------------------------------------------------------------
    U = u(:)*1536;
    
else
    % exogenous input
    %----------------------------------------------------------------------
    U = C*u(:)*32;
    
end