function [new_header] = setparameter(header, parameter, value, index)
%SETPARAMETER  Set the value of a specified header parameter. 
%
%	NEW_HEADER = SETPARAMETER(HEADER, PARAMETER, VALUE, INDEX)
%
%       PARAMETERS: 1) The header in which to set the new parameter value.
%                   2) The parameter name as a string.
%		    3) The value to set.
%		    4) The index of the parameter to be set. If not
%		       defined, all the parameters will be changed.
%
%	If the parameter does not exist, it will be appended to
%	the header.
%
%       RETURN:     On success, return the modified header else return
%		    an empty matrix.
%                   
%       Claudio  6 May 1994. Modified 7 April 1995 by Mark to fix a problem
% 			when two parameters have the same value

%
% Copyright (c) 1995 by Claudio Rivetti and Mark Young
% claudio@alice.uoregon.edu,    mark@alice.uoregon.edu
%


if nargin<3
  error('Too few input arguments');
end
if nargin>4
  error('Too many input arguments');
end

header = char(header);
EOF     = char(26);
AlexNEWLINE = char(13);
new_header = [];
sep='';
i=1;

if isempty(header)
  return;
end

if nargin==3
  index=0;
end

hlen=length(header);

str_value=[];
if ~isstr(value)
  for i=1:length(value)
    str_value=[str_value, num2str(value(i)), ' '];
  end
else
  str_value=value;
end

if ~isempty(str_value)
  str_value = deblank(str_value);
  str_value = deblank(fliplr(str_value));
  str_value = fliplr(str_value);
  sep=': ';
end
parameter = strrep(parameter, ':', '');
parameter = strrep(parameter, '\', '');
parameter = deblank(parameter);
parameter = deblank(fliplr(parameter));
parameter = fliplr(parameter);


cs=findstr(header, ': ');
nl=find(header == AlexNEWLINE);

p1=findstr(upper(header), upper(['\' parameter ':']));

  parameter(1)=upper(parameter(1));

% if the parameter does not exist it will be added
% at the end of the Header.

if isempty(p1)
  parval=['\', parameter, sep, str_value, AlexNEWLINE 10 AlexEOF];
  new_header=strrep(header, AlexEOF, parval);
else  
  for i=1:length(p1)
    p2=[p2 min(find(cs>p1(i)))];
    p3=[p3 min(find(nl>p1(i)))];
  end

  p2=cs(p2);
  p3=nl(p3)-1;
  str_value = ['\' parameter sep str_value];
  if index
    new_header=strrep(header, header(p1(index):p3(index)), str_value);
  else
    new_header=header;
    for i=1:length(p1)
      new_header=strrep(new_header, header(p1(i):p3(i)), str_value);
    end
  end
end

% Truncate or add zeros at the end of the header in order to keep
% the same header size.
newhlen=length(new_header);
if newhlen > hlen
  new_header=new_header(1:hlen);
else
  new_header=[new_header zeros(1,hlen-newhlen)]; 
end

return;