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_MDP_VB_LFP.m
    path of file: ./repos/spm12/toolbox/DEM
    
    the code of the file until where you have to start completion: function [u,v] = spm_MDP_VB_LFP(MDP,UNITS,f,SPECTRAL)
% auxiliary routine for plotting simulated electrophysiological responses
% FORMAT [u,v] = spm_MDP_VB_LFP(MDP,UNITS,FACTOR,SPECTRAL)
%
% MDP        - structure (see spm_MDP_VB_X.m)
%  .xn       - neuronal firing
%  .dn       - phasic dopamine responses

    
function [u,v] = spm_MDP_VB_LFP(MDP,UNITS,f,SPECTRAL)
% auxiliary routine for plotting simulated electrophysiological responses
% FORMAT [u,v] = spm_MDP_VB_LFP(MDP,UNITS,FACTOR,SPECTRAL)
%
% MDP        - structure (see spm_MDP_VB_X.m)
%  .xn       - neuronal firing
%  .dn       - phasic dopamine responses
%
% UNITS(1,j) - hidden state                           [default: all]
% UNITS(2,j) - time step
%
% FACTOR     - hidden factor to plot                  [default: 1]
% SPECTRAL   - replace raster with spectral responses [default: 0]
%
% u - selected unit rate of change of firing (simulated voltage)
% v - selected unit responses {number of trials, number of units}
%
% This routine plots simulated electrophysiological responses. Graphics are
% provided in terms of simulated spike rates (posterior expectations).
%
% see also: spm_MDP_VB_ERP (for hierarchical belief updating)
%__________________________________________________________________________
% Copyright (C) 2005 Wellcome Trust Centre for Neuroimaging
 
% Karl Friston
% $Id: spm_MDP_VB_LFP.m 7760 2019-12-29 17:45:58Z karl $
 
 
% defaults
%==========================================================================
try, f;          catch, f        = 1;  end