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: VBA_spm_fieldindices.m
    path of file: ./repos/VBA-toolbox/thrid-party/spm
    
    the code of the file until where you have to start completion: function [ix] = VBA_spm_fieldindices(X,varargin)
% Return the indices of fields in a structure (and vice versa)
% FORMAT [i]     = spm_fieldindices(X,field1,field2,...)
% FORMAT [field] = spm_fieldindices(X,i1,i2,...)
%
% X         - structure
% field1,.. - fields
%
% i         - vector of indices or feildname{s}
%
%__________________________________________________________________________
% Copyright (C) 2010-2013 Wellcome Trust Centre for Neuroimaging

% Karl Friston
% $Id: spm_fieldindices.m 5769 2013-11-27 19:37:01Z karl $


% if varargin is a vector simply return fieldnames
%--------------------------------------------------------------------------
if nargin == 2

    
function [ix] = VBA_spm_fieldindices(X,varargin)
% Return the indices of fields in a structure (and vice versa)
% FORMAT [i]     = spm_fieldindices(X,field1,field2,...)
% FORMAT [field] = spm_fieldindices(X,i1,i2,...)
%
% X         - structure
% field1,.. - fields
%
% i         - vector of indices or feildname{s}
%
%__________________________________________________________________________
% Copyright (C) 2010-2013 Wellcome Trust Centre for Neuroimaging

% Karl Friston
% $Id: spm_fieldindices.m 5769 2013-11-27 19:37:01Z karl $


% if varargin is a vector simply return fieldnames
%--------------------------------------------------------------------------
if nargin == 2
   if isnumeric(varargin{1})
       if numel(varargin{1}) > 1
           for j = 1:length(varargin{1})
               ix{j} = VBA_spm_fieldindices(X,varargin{1}(j));
           end