New Features
in
DFIELD & PPLANE
for
MATLAB version 5.2

These revisions incorporate one important new feature, a number of smaller ones, and the correction of some code in pplane5 which lead to warnings. The changes are not substantial enough to call for a name change, so they are still called dfield5 and pplane5.

New features common to both.

Expressions as well as parameters. It is now possible to enter mathematical expressions into the edit boxes that used to be limited to parameters. The expressions can involve the problem variables only and not other parameter or expressions. This means that the independent variable can be used in dfield5 but not in pplane5.

New method to change default settings. I have been experimenting with different ways of allowing the user to change some of the defaults. This is the best way I have found to date. It uses an optional startup file. These are different for the two routines, and they will be explained in more detail in what follows.

New features in dfield5.

Maximum stepsize as a solver option. This parameter can be set using the Solver Settings option. It is for those times that you want to be sure that the solver does not take hughe steps.

New method to change default settings. This requires the use of an optional auxillary file with the name dfstart.m. Here is an example of such a file: 

function H = dfstart

% DFSTART is a function m-file that is read when DFIELD5 
%         is started and which inputs certain data that 
%         are used to change defaults.  Only four items 
%         may be changed.  To do so it is necessary to enter 
%         one or more of the following lines.  The entries 
%         here are the defaults.

H = [];   % DO NOT REMOVE THIS LINE!
          % If there is a dfstart.m file, it must contain this line.


% H.style = 'display';	% Must be 'white', 'black', or 'display'. 
                        % 'white' is the default.
                     

% H.size = 15;	     % Any number is allowed.  This is the 
                     % main font size used in DFIELD5.  It 
                     % determines the size of all windows,
                     % and everything else.
		     % The default is 10
                     
% H.npts = 20;       % The number of field points per line.  
                     % The default = 20.

% H.solver = 'Euler';  % The choices are 'Euler', 'Runge-Kutta 2', 
                       % 'Runge-Kutta 2', and 'Dormand-Prince'.
		       % The default is 'Dormand-Prince'.

As can be seen, it is possible to change only four of the defaults. To change a default it is necessary to remove the comment character (%) from the appropriate line. The defaults that can be changed and the options are:

style This determines the appearance of dfield5. The options are 'white', 'black', and 'display'. 'white' is the default option and is the same as the default MATLAB option. 'black' makes the backgrounds of the figures black. 'display' a modification of 'white' which we have found is more suitable for use with a computer projection system.
size This parameter determines the size of all the winodws. It refers to the main point size used for the text, but everyting else is resized accordingly. The default is 10. 15 is good for use with a projection system. dfield5 will ensure that no figure is too large to fit on the screen.
npts This is the number of field points per line in the dfield5 Display window. The default is 20.
solver The user can choose the default solver that is used to solve the ODEs. The options are 'Dormand-Prince' (this is the default), 'Runge-Kutta 4', 'Runge-Kutta 2', and 'Euler'.

New features in pplane5.

Runge-Kutta 4 solver. This is a standard fourth order Runge-Kutta solver.

New method to change default settings. This requires the use of an optional auxillary file with the name ppstart.m. Here is an example of such a file: 

function H = ppstart

% PPSTART is a function m-file that is read when PPLANE5 
%         is started and which inputs certain data that 
%         are used to change defaults.  Only three items 
%         allowed.  If only one item is to be changed, all 
%         three should be included.  The following are the 
%         defaults as written in PPLANE5, and changes can 
%         be made as needed.

H =[];     % DO NOT REMOVE THIS LINE!
           % This command is essential to the working of this function.  It
           % is necessary if this file exists, even if no changes follow it.
	   
% H.style = 'display';	% Choices are 'white','black', or 'display', 
                        % The default is 'white'.

% H.size = 15;	     % Any number is allowed.  This is the 
                     % main font size used in PPLANE5.  It 
                     % determines the size of all windows,
                     % and everything else.  The default is 10.

%H.ppdir = 'c:\matlab';		% The directory where systems and 
                  % galleries are to be found.  This must be 
                  % a string like:
                  %    'c:\Matlab\files'   (PC)
                  %    '/home/polking/matlab/files'  (UNIX)
                  %    'Macintosh HD:Matlab:files'   (Mac)                  

%H.npts = 15;   % The number of field points per line.  The default is 20.

% H.solver = 'Runge-Kutta 4';  % The choices are 'Dormand Prince', 'ode15s',
                              % and 'Runge-Kutta 4'.  The default is 
			      % 'Dormand Prince'.
			      
% H.tolerance = 1e-5;  % The tolernace used by the Dormand Prince and ode15s
                     % solvers.  It should be at most 1e-3 and at least
                     % 1e-12.  The default is 5e-4.
		     
% H.stepsize = 0.01;   % The step size used by the Runge-Kutta 4 solver.
                     % The default is 0.1;

As can be seen, it is possible to change only some of the defaults. To change a default it is necessary to remove the comment character (%) from the appropriate line. The defaults that can be changed and the options are:

style This determines the appearance of pplane5. The options are 'white', 'black', and 'display'. 'white' is the default option and is the same as the default MATLAB option. 'black' makes the backgrounds of the figures black. 'display' a modification of 'white' which we have found is more suitable for use with a computer projection system.
size This parameter determines the size of all the winodws. It refers to the main point size used for the text, but everyting else is resized accordingly. The default is 10. 15 is good for use with a projection system. pplane5 will ensure that no figure is too large to fit on the screen.
npts This is the number of field points per line in the pplane5 Display window. The default is 20.
solver The user can choose the default solver that is used to solve the ODEs. The options are 'Dormand-Prince' (this is the default), 'Runge-Kutta 4', 'Runge-Kutta 2', and 'Euler'.
ppdir This is the the directory in which pplane5 looks first for systems and galleries. This must be a string like: 
                'c:\Matlab\files'   (PC)
                '/home/polking/matlab/files'  (UNIX)
                'Macintosh HD:Matlab:files'   (Mac)
tolerance The tolerance used by the Dormand Prince and ode15s solvers. It should be at most 1e-3 and at least 1e-12. The default is 5e-4. It is not at all unreasonable to set this to be something like 1e-5 or 1e-6.
stepsize The step size used by the Runge-Kutta 4 solver. The default is 0.1;

John C. Polking <polking@rice.edu>
Last modified: Mon Oct 26 09:25:25 Central Standard Time 1998