defval.m

function defval(name,value)
% DEFVAL(name,value)
%
% Assigns a default value to the named variable
%
% INPUT:
% 
% name    A string, enclosed in single quotes, with a variable name
% value   The value, whatever it is, that you want the variable to have 
%
% OUTPUT:
%
%      None. The variables appear as if by magic into your workspace or
%      will be available inside your function.
%
% NOTE: 
%
% This won't work for an unassigned structure variable.
%
% Last modified by ebrevdo-at-alumni-princeton.edu, 05/28/2011
% Last modified by fjsimons-at-alum.mit.edu, 12/20/2012
% 
% It appears that defval('bla',functioncall) evaluates the function call
% regardless of whether or not 'bla' has been assigned.

if ~ischar(name),
  error(sprintf(['The first argument of DEFVAL ',...
		'has to be a string with a variable name']));
end

% Always do it is our default here
si=1;
% If it exists... as a variable (say it, it makes it faster!)
if evalin('caller',[ 'exist(''' name ''',''var'')']);
  % ... and it's empty, do it; but don't do it if it's non empty
  si=evalin('caller',[ 'isempty(' name ')']);
end
% Do it or not
if si
  assignin('caller',name,value);
end