--- /dev/null
+## Copyright (C) 2006,2007,2008 Carlo de Falco, Culpo Massimiliano
+##
+## 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>
+## author: culpo@math.uni-wuppertal.de
+
+## -*- texinfo -*-
+##
+## @deftypefn{Function File} {[@var{A},@var{B},@var{C}] =}@
+## asm_initialize_system(@var{instruct},@var{x})
+##
+## Cycle through the circuit description structure @var{instruct}
+## to build the system matrices @var{A}, @var{B}, @var{C} for
+## the linear and time-invariant part of the system.
+##
+## @var{x} is the current value of the state variables.
+##
+## See the @cite{IFF file format specifications} for details about
+## the output matrices.
+##
+## @seealso{asm_build_system,prs_iff}
+##
+## @end deftypefn
+
+function [A,B,C] = asm_initialize_system(instruct,x);
+
+ ## Check input
+ if nargin != 2
+ error("asm_initialize_system: wrong number of input parameters.");
+ elseif !(isstruct(instruct) && isfield(instruct,"LCR") &&
+ isfield(instruct,"NLC"))
+ error("asm_initialize_system: first input is not a valid structure.");
+ elseif !isvector(x)
+ error("asm_initialize_system: second input is not a valid vector.");
+ endif
+
+ ## Build linear part of the system
+ n = instruct.totextvar + instruct.totintvar; # Number of variables
+
+ ## Initialize to zero any state variable that is not in the input argument
+ lx = length(x);
+ if lx < n
+ x(lx+1:n) = 0;
+ endif
+ ## FIXME: should a warning be passed if lx != n ?
+
+ A = sparse(n,n);
+
+ ## LCR section
+ B = sparse(n,n);
+ C = sparse(n,1);
+
+ nblocks = length(instruct.LCR);
+
+ for ibl = 1:nblocks
+ for iel = 1:instruct.LCR(ibl).nrows
+
+ ## Evaluate element
+ if instruct.LCR(ibl).nintvar(iel)
+ intvars = instruct.totextvar + instruct.LCR(ibl).osintvar(iel) + [1:instruct.LCR(ibl).nintvar(iel)]';
+ else
+ intvars=[];
+ endif
+
+ il = instruct.LCR(ibl).vnmatrix(iel,:)';
+ nzil = find(il!=0);
+
+ y = zeros(size(il));
+ y(nzil) = x(il(nzil));
+ z = x(intvars);
+
+ [a,b,c] = feval(instruct.LCR(ibl).func,
+ instruct.LCR(ibl).section,
+ instruct.LCR(ibl).pvmatrix(iel,:),
+ instruct.LCR(ibl).parnames,
+ y,z,0);
+
+ ## Assemble matrices
+
+ ## Global indexing
+ vars = [il(nzil);intvars];
+
+ ## Local indexing
+ lclvars = [nzil; instruct.LCR(ibl).nextvar + (1:length(intvars))' ];
+
+ ## Reshaping sparse stamps
+ a = a(lclvars,lclvars);
+ b = b(lclvars,lclvars);
+ c = reshape(c(lclvars),[],1);
+
+ [na,ma,va] = find(a);
+ [nb,mb,vb] = find(b);
+ [nc,mc,vc] = find(c);
+
+ ## Stamping
+ A += sparse(vars(na),vars(ma),va,n,n);
+ B += sparse(vars(nb),vars(mb),vb,n,n);
+ C += sparse(vars(nc),1,vc,n,1);
+
+ endfor
+ endfor
+
+endfunction
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