function options = ddeset(varargin)
%DDESET  Create/alter DDE OPTIONS structure.
%   OPTIONS = DDESET('NAME1',VALUE1,'NAME2',VALUE2,...) creates an integrator
%   options structure OPTIONS in which the named properties have the
%   specified values. Any unspecified properties have default values. It is
%   sufficient to type only the leading characters that uniquely identify the
%   property. Case is ignored for property names. 
%   
%   OPTIONS = DDESET(OLDOPTS,'NAME1',VALUE1,...) alters an existing options
%   structure OLDOPTS.
%   
%   OPTIONS = DDESET(OLDOPTS,NEWOPTS) combines an existing options structure
%   OLDOPTS with a new options structure NEWOPTS. Any new properties
%   overwrite corresponding old properties. 
%   
%   DDESET with no input arguments displays all property names and their
%   possible values.
%   
%DDESET PROPERTIES
%   
%RelTol - Relative error tolerance  [ positive scalar {1e-3} ]
%   This scalar applies to all components of the solution vector, and
%   defaults to 1e-3 (0.1% accuracy).  The estimated error in each 
%   integration step satisfies e(i) <= max(RelTol*abs(y(i)),AbsTol(i)).
%
%AbsTol - Absolute error tolerance  [ positive scalar or vector {1e-6} ]
%   A scalar tolerance applies to all components of the solution vector.
%   Elements of a vector of tolerances apply to corresponding components of
%   the solution vector.  AbsTol defaults to 1e-6.
%
%NormControl - Control error relative to norm of solution  [ on | {off} ]
%   Set this property 'on' to request that the solver controls the error in
%   each integration step with norm(e) <= max(RelTol*norm(y),AbsTol). By
%   default the solver uses a more stringent component-wise error control. 
%
%Events - Locate events  [ function_handle ]
%   To detect events, set this property to the event function.
%   
%InitialStep - Suggested initial step size  [ positive scalar ]
%   The solver will try this first.  By default the solver determines an
%   initial step size automatically.
%
%MaxStep - Upper bound on step size  [ positive scalar ]
%   MaxStep defaults to one-tenth of the tspan interval.
%   
%OutputFcn - Installable output function  [ function_handle ]
%   This output function is called by the solver after each time step. When
%   the solver is called with no output arguments, OutputFcn defaults to 
%   @odeplot. Otherwise, OutputFcn defaults to [].
%   
%OutputSel - Output selection indices  [ vector of integers ]
%   This vector of indices specifies which components of the solution vector
%   are passed to the OutputFcn. OutputSel defaults to all components.
%   
%Stats - Display computational cost statistics  [ on | {off} ]
%   
%InitialY - Initial value of solution [ vector ]
%   By default the initial value of the solution is the value returned by
%   HISTORY at the initial point.  A different initial value can be supplied
%   as the value of the InitialY property.
%
%Jumps - Discontinuities in solution [ vector ]
%   Points t where the history or solution may have a jump discontinuity
%   in a low order derivative.
%   
%   See also DDEGET, DDE23, FUNCTION_HANDLE.

%   Copyright 1984-2003 The MathWorks, Inc. 
%   $Revision: 1.3.4.3 $  $Date: 2004/12/06 16:34:18 $

% Print out possible values of properties.
if (nargin == 0) && (nargout == 0)
  fprintf('          AbsTol: [ positive scalar or vector {1e-6} ]\n');
  fprintf('          Events: [ function_handle ]\n');
  fprintf('     InitialStep: [ positive scalar ]\n');
  fprintf('        InitialY: [ vector ]\n');
  fprintf('           Jumps: [ vector ]\n');  
  fprintf('         MaxStep: [ positive scalar ]\n');
  fprintf('     NormControl: [ on | {off} ]\n');
  fprintf('       OutputFcn: [ function_handle ]\n');
  fprintf('       OutputSel: [ vector of integers ]\n');
  fprintf('          RelTol: [ positive scalar {1e-3} ]\n');
  fprintf('           Stats: [ on | {off} ]\n');
  fprintf('\n');
  return;
end

Names = [
         'AbsTol      '    
         'Events      '
         'InitialStep '
         'InitialY    '
         'Jumps       '
         'MaxStep     '
         'NormControl '
         'OutputFcn   '
         'OutputSel   '
         'RelTol      '
         'Stats       '         
                       ];
m = size(Names,1);
names = lower(Names);

% Combine all leading options structures o1, o2, ... in ddeset(o1,o2,...).
options = [];
for j = 1:m
  options.(deblank(Names(j,:))) = [];
end
i = 1;
while i <= nargin
  arg = varargin{i};
  if ischar(arg)                         % arg is an option name
    break;
  end
  if ~isempty(arg)                      % [] is a valid options argument
    if ~isa(arg,'struct')
      error('MATLAB:ddeset:NoPropNameOrStruct',...
            ['Expected argument %d to be a string property name ' ...
             'or an options structure\ncreated with DDESET.'], i);
    end
    for j = 1:m
      if any(strcmp(fieldnames(arg),deblank(Names(j,:))))
        val = arg.(deblank(Names(j,:)));
      else
        val = [];
      end
      if ~isempty(val)
        options.(deblank(Names(j,:))) =  val;
      end
    end
  end
  i = i + 1;
end

% A finite state machine to parse name-value pairs.
if rem(nargin-i+1,2) ~= 0
  error('MATLAB:ddeset:ArgNameValueMismatch',...
        'Arguments must occur in name-value pairs.');
end
expectval = 0;                          % start expecting a name, not a value
while i <= nargin
  arg = varargin{i};
    
  if ~expectval
    if ~ischar(arg)
      error('MATLAB:ddeset:InvalidPropName',...
            'Expected argument %d to be a string property name.', i);
    end
    
    lowArg = lower(arg);
    j = strmatch(lowArg,names);
    if isempty(j)                       % if no matches
      error('MATLAB:ddeset:InvalidPropName',...
            'Unrecognized property name ''%s''.', arg);
    elseif length(j) > 1                % if more than one match
      % Check for any exact matches (in case any names are subsets of others)
      k = strmatch(lowArg,names,'exact');
      if length(k) == 1
        j = k;
      else
        msg = sprintf('Ambiguous property name ''%s'' ', arg);
        msg = [msg '(' deblank(Names(j(1),:))];
        for k = j(2:length(j))'
          msg = [msg ', ' deblank(Names(k,:))];
        end
        msg = sprintf('%s).', msg);
        error('MATLAB:ddeset:AmbiguousPropName', msg);
      end
    end
    expectval = 1;                      % we expect a value next
    
  else
    options.(deblank(Names(j,:))) = arg;
    expectval = 0;
      
  end
  i = i + 1;
end

if expectval
  error('MATLAB:bvpset:NoValueForProp',...
        'Expected value for property ''%s''.', arg);
end