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_dcm_erp_update.m
    path of file: ./repos/spm/toolbox/dcm_meeg
    
    the code of the file until where you have to start completion: function DCM = spm_dcm_erp_update(DCM,oldDCM,fields)

    
function DCM = spm_dcm_erp_update(DCM,oldDCM,fields)
% Set priors over DCM model parameters for Bayesian updating
% FORMAT DCM = spm_dcm_erp_update(DCM,oldDCM,fields)
%
% DCM    - DCM structure to be updated
% oldDCM - inverted DCM with posterior moments
% fields - character array of fields to be updated: e.g.,{'A','B'}
%__________________________________________________________________________

% Karl Friston
% Copyright (C) 2005-2022 Wellcome Centre for Human Neuroimaging

% get prior structure for the sort of model
%==========================================================================
try, model = DCM.options.model; catch, model = 'CMC'; end