#
 #  Simple calculator for an R-2R Resistor Ladder with any R/R2 ratio
 #
 #  Copyright (C) 2010  Clifford Wolf <clifford@clifford.at>
 #
 #  This program 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; either version 2 of the License, or
 #  (at your option) any later version.
 #
 #  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; if not, write to the Free Software
 #  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 #

function ulist = r2rcalc(u, r1, r2, n)

	#  Circuit Topology:
	#
	#  GND --[R2]--*--[R1]--*--[R1]--*--[R1]--*-- ..... --*-- OUTPUT
	#              |        |        |        |           |
	#            [R2]     [R2]     [R2]     [R2]        [R2]
	#              |        |        |        |           |
	#             U1       U2       U3       U4          Un

	Mr1 = zeros(n);

	for i = 1:n
	for j = 1:n
		Mr1(i,j) = min(i,j)-1;
	endfor
	endfor

	Mr2 = ones(n) + eye(n);

	M = Mr1*r1 + Mr2*r2;

	# printf("System Matrix:\n");
	# disp(M);

	ulist = ones(1, 2^n);
	for i = 0:(2^n-1)
		Us = bitget(i, 1:n)'*u;
		Is = M \ Us;
		U = ((0:n-1)*r1 + ones(1,n)*r2) * Is;
		ulist(i+1) = U;
		# printf("\n-- %d --\n", i);
		# printf("Us:\n");
		# disp(Us);
		# printf("Is:\n");
		# disp(Is);
		# printf("U:\n");
		# disp(U);
	endfor

endfunction

# Usage example:
# plot(r2rcalc(5, 100, 220, 6));