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: readmarbletrj.m
    path of file: ./repos/mdtoolbox/mdtoolbox
    
    the code of the file until where you have to start completion: function [trj, box, vel] = readmarbletrj(filename, index_atom, index_time)
%% readmarbletrj
% read marble ascii-format trajectory file
%
%% Syntax
%# trj = readmarbletrj(filename);
%# trj = readmarbletrj(filename, index_atom);
%# trj = readmarbletrj(filename, index_atom, index_time);
%# [trj, box] = readmarbletrj(filename, index_atom, index_time);
%# [trj, box, vel] = readmarbletrj(filename, index_atom, index_time);
%
%% Description
% The XYZ coordinates of atoms are read into 'trj' variable
% which has 'nframe' rows and '3*natom' columns.
% Each row of 'trj' has the XYZ coordinates of atoms in order 
% [x(1) y(1) z(1) x(2) y(2) z(2) ... x(natom) y(natom) z(natom)].
%
% * filename   - input marble trajectory filename
% * index_atom - atom index or logical index specifying atoms to be read
% * index_time - time index or logical index specifying time frames to be read
% * trj        - trajectory [nframex3natom double]
% * box        - box size [nframex3 double]
% * vel        - velocities [nframex3natom double]
%
%% Example
%# trj = readmarbletrj('eq.trj');
%
%% See alo
% readmarbletrjbin
% readmarblecrd
%


    
function [trj, box, vel] = readmarbletrj(filename, index_atom, index_time)
%% readmarbletrj
% read marble ascii-format trajectory file
%
%% Syntax
%# trj = readmarbletrj(filename);
%# trj = readmarbletrj(filename, index_atom);
%# trj = readmarbletrj(filename, index_atom, index_time);
%# [trj, box] = readmarbletrj(filename, index_atom, index_time);
%# [trj, box, vel] = readmarbletrj(filename, index_atom, index_time);
%
%% Description
% The XYZ coordinates of atoms are read into 'trj' variable
% which has 'nframe' rows and '3*natom' columns.
% Each row of 'trj' has the XYZ coordinates of atoms in order 
% [x(1) y(1) z(1) x(2) y(2) z(2) ... x(natom) y(natom) z(natom)].
%
% * filename   - input marble trajectory filename
% * index_atom - atom index or logical index specifying atoms to be read
% * index_time - time index or logical index specifying time frames to be read
% * trj        - trajectory [nframex3natom double]
% * box        - box size [nframex3 double]
% * vel        - velocities [nframex3natom double]
%
%% Example
%# trj = readmarbletrj('eq.trj');
%
%% See alo
% readmarbletrjbin
% readmarblecrd
%

%% initialization
is_trj = false;
is_box = false;
is_vel = false;

if ~exist('index_time', 'var') || isempty(index_time)
  index_time = [];
end