function obvod
U0 = 50;
R1 = 15; R2 = 10; R3 = 16; R4 = 3; R5 = 7; R6 = 12;
R7 = 1; R8 = 9; R9 = 11; R10 = 9; R11 = 14; R12 = 12;
R67=R6*R7/(R6+R7);
A=[1,-1,-1,0,0,0,0,0;...
    0,0,1,1,0,0,0,1;...
    -1,0,0,0,1,-1,0,0;...
   0,0,0,0,0,1,-1,-1;...
   R1+R2,R3,0,0,R67+R8,0,0,0;...
   0,-R3,R4,-R5,0,0,0,0;...
   0,0,0,0,-R5];

end

