function x = ninetothree(xold)
% This function computes the restriction of a level 1 Y-network of
% resistors to a single Y-circuit, as shown below:
%
%      |
%     / \        ->       |
%    |   |               / \
%   / \ / \

x1 = xold(1,:) ;
x2 = xold(2,:) ;
x3 = xold(3,:) ;

y1 = x2(3) + x3(2) ;
y2 = x1(3) + x3(1) ;
y3 = x2(1) + x1(2) ;

y = deltay([y1 y2 y3]) ;

x(1) = y(1) + x1(1) ;
x(2) = y(2) + x2(2) ;
x(3) = y(3) + x3(3) ;
