dydt(t, y, yp, rpar)

function [dev,ires] = dydt(t, y, yp, rpar)
%
% dydt function
%___________________________________________________________________________
%___________________________________________________________________________
%
% Edited by: Giovani Tonel, Taking Master Degree in Chemical Engineering
% Chemical Engineering Department - GIMSCOP/ALSOC
% Federal University of Rio Grande do Sul - UFRGS
% Porto Alegre, RS - Brazil
% Phone: [phone] (GIMSCOP - Room 2)
% Email address: [e-mail]  
% Website: http://www.enq.ufrgs.br/gimscop
% October 2007; Last revision: 15-October-2007
%___________________________________________________________________________
%___________________________________________________________________________

global DEBUG;


% only for test
a1      =   rpar(1) ;
b2      =   rpar(2) ;
%********************

plot_do = 0;

if plot_do
    %########################################################################
    %
    % solving a DAE problem
    %
    dev(1)  =   yp(1) + 4*y(1)+ 0*a1         ;
    dev(2)  =   yp(2) + 6*y(2)+ 0*b2         ;
    dev(3)  =   y(3) - y(1)-2.0              ;
    %
    %########################################################################
    %
    %
else 
    %########################################################################
    %
    % solving a ODE problem(dxdt)
    %
    dev(1)  =   yp(1) + 4*y(1)        ;
    dev(2)  =   yp(2) + 6*y(2)        ;
    dev(3)  =   yp(3) - y(1)-2.0      ;
    %
    %########################################################################
end

    

ires    = 0;

%         IRES is an integer flag which is always equal to
%         zero on input. Subroutine RES should alter IRES
%         only if it encounters an illegal value of Y or
%         a stop condition. Set IRES = -1 if an input value
%         is illegal, and DDASSL will try to solve the problem
%         without getting IRES = -1. If IRES = -2, DDASSL
%         will return control to the calling program
%         with IDID = -11.

if ( DEBUG > 9 )
  buf1 = sprintf('%.4e ',y);
  buf2 = sprintf('%.4e ',yp);
  buf3 = sprintf('%.4e ',dev);
  disp(sprintf('(Debug) dydt.m: t=%.2e y=%s yp=%s dev=%s', t,buf1,buf2,buf3));
  if ( DEBUG > 99 )
    cbuf = input(sprintf('\tRETURN to continue : '));
  end
end