% Electric circuit, 2 loops, 4 nodes, Electr1.m
clear                       % variables
format short e
volt1 = 20
volt4 = 0

k12 = 1/4;
k23 = 1;
k24 = 1/8;
k34 = 1/3;
k22 = k12 + k23 + k24;
k33 = k23 + k34;
k44 = k24 + k34;
beta = k12*1e7              % zienk factor

stiff = [ k12    -k12     0     0    % cond matrix
         -k12     k22   -k23   -k24
          0      -k23    k33   -k34
          0      -k24   -k34    k44  ];
df =   [ volt1*beta; 0; 0; volt4*beta ]   % combined d, F
zienk = stiff;
zienk(1,1)=zienk(1,1)+beta;
zienk(4,4)=zienk(4,4)+beta
format short
volts = inv(zienk) * df;       % displacements
current = stiff * volts        % force vector

% print the results
fprintf('\n       Electric 4x4 ')
fprintf('\n   Your name, MENG 421, ')
disp(date)

fprintf('\n   Node     Volts    Current\n')
for i = 1:length(df)
  fprintf('    %2.0f   %7.1f   %7.1f \n',i,volts(i),current(i))
end

%      Electric 4x4
%  Your name, MENG 421, 01-Apr-2004

%  Node     Volts     Current
%    1      20.0       3.0
%    2       8.0       0.0
%    3       6.0       0.0
%    4       0.0      -3.0