--- /dev/null
+## Copyright (C) 2006,2007,2008 Carlo de Falco
+##
+## This file is part of:
+## OCS - A Circuit Simulator for Octave
+##
+## OCS is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program (see the file LICENSE); if not,
+## see <http://www.gnu.org/licenses/>.
+##
+## author: Carlo de Falco <cdf _AT_ users.sourceforge.net>
+
+## -*- texinfo -*-
+##
+## @deftypefn{Function File} {[@var{out},@var{niter}] =} tst_theta_method @
+## (@var{cirstruct},@var{x},@var{t},@var{tol},@
+## @var{maxit},@var{theta},@var{pltvars},@
+## @var{verbosity});
+##
+## Perform a transient simulation of the system described by
+## @var{cirstruct} over the time interval @var{t} using the
+## theta-method with parameter @var{theta}.
+##
+## The initial value for the state vector is computed by solving a
+## steady state problem at @var{t}(1), with starting guess @var{x}.
+##
+## @var{tol} and @var{maxit} are parameters passed to
+## @code{nls_newton_raphson}.
+##
+## The output @var{out} will contain the value of the state vector at
+## each point of @var{t}.
+##
+## The optional parameter @var{verbosity} controls the amount of
+## output produced:
+##
+## @itemize @minus
+## @item if verbosity(1) != 0, information on the progress
+## of the algorithm are output at runtime
+## @item if verbosity(2) != 0, the plot of the variables whose names
+## are listed in @var{pltvars} is
+## produced after the computation
+## @end itemize
+##
+## The optional output @var{niter} returns the number of Newton iterations
+## needed to reach convergence.
+##
+## @seealso{tst_backward_euler,tst_daspk,tst_odepkg,nls_newton_raphson}
+##
+## @end deftypefn
+
+function [out, varargout] = tst_theta_method(outstruct,x,t,tol,maxit,\
+ theta,pltvars,verbosity)
+
+ ## Check input
+ ## FIXME: add input check!
+ if ((nargin < 7) || (nargin > 8))
+ error("tst_theta_method: wrong number of input parameters.");
+ endif
+
+ if ~exist("verbosity")
+ verbosity = [0,0];
+ elseif length(verbosity)<2
+ verbosity(2) = 0;
+ endif
+
+ out = zeros(rows(x),columns(t));
+ out(:,1) = x;
+
+ if nargout > 1
+ niter = zeros(length(t),1);
+ endif
+
+ if (verbosity(1))
+ fprintf(1,"Initial value.\n");
+ endif
+
+
+ [A0,B,C] = asm_initialize_system(outstruct,x);
+
+ [out(:,1),ii] = nls_stationary(outstruct,x,tol,maxit);
+
+ if nargout > 1
+ niter(1) = ii;
+ endif
+
+ for it=2:length(t)
+
+ if(verbosity)
+ fprintf(1,"Timestep #%d.\n",it);
+ endif
+
+
+ [A1old,Jacold,resold] = asm_build_system(outstruct, out(:,it-1), t(it-1));
+
+ JAC = @(x,A1,Jac,res) TSTTHETAFUNJAC1(outstruct, x, t(it-1),
+ t(it), A0, B, theta,
+ A1, Jac, res);
+ RES = @(x,A1,Jac,res) TSTTHETAFUNRES1(outstruct, x, out(:,it-1),
+ t(it-1), t(it), A0, B, C,
+ resold, theta, A1, Jac, res);
+ UPDT = @(x) TSTTHETAFUNUP1 (outstruct, x, t(it));
+
+ [out(:,it),ii,resnrm] = nls_newton_raphson(out(:,it-1),RES,JAC,\
+ tol, maxit,verbosity(1),\
+ UPDT);
+
+ if nargout > 1
+ niter(it) = ii;
+ endif
+
+ if (verbosity(2))
+ utl_plot_by_name(t(1:it),out(:,1:it),outstruct,pltvars);
+ pause(.1);
+ endif
+
+ if exist("~/.stop_ocs","file")
+ break
+ end
+ endfor
+
+ if nargout > 1
+ varargout{1} = niter;
+ endif
+
+endfunction
+
+## Jacobian for transient problem
+function lhs = TSTTHETAFUNJAC1(outstruct, x, t0, t1, A0, B, theta, A1, Jac, res)
+
+ DT = t1-t0;
+ if ( nargin < 10 )
+ [A1,Jac,res] = asm_build_system(outstruct,x,t1);
+ endif
+ lhs = ( (A0+A1)/DT + theta*(B + Jac) );
+
+endfunction
+## Residual for transient problem
+function rhs = TSTTHETAFUNRES1(outstruct, x, xold, t0, t1, A0, B, C,
+ resold, theta, A1, Jac, res)
+ DT = t1-t0;
+ if ( nargin < 13 )
+ [A1,Jac,res] = asm_build_system(outstruct,x,t1);
+ endif
+ rhs = ( (A1+A0)*(x-xold)/DT + theta * (res + C + B*x) +
+ (1-theta) * (resold + C + B*xold) );
+
+endfunction
+## Update for transient problem
+function update = TSTTHETAFUNUP1(outstruct,x,t1)
+
+ [A1,Jac,res] = asm_build_system(outstruct,x,t1);
+ update = {A1,Jac,res};
+
+endfunction
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