R1 = 1;
R2 = 1;
R3 = 1;
R4 = 1;
R5 = 1;
R6 = 1;
R7 = 1;

E1 = 10;
E2 = 20;
E3 = 30;
E4 = 40;

I1 = 1;

A = [((1/R4)+(1/R2)+(1/R7)) (-(1/R7)) (-(1/R2)); 
	 (-(1/R7)) ((1/R7)+(1/R4)+(1/R5)+(1/R6)) (-(1/R4));
	 (-(1/R2)) (-(1/R4)) ((1/R2)+(1/R3)+(1/R4))];
     
B = [(-(E3/R7)-(E1/R1));
	 ((E2/R6)-(E1/R5)+(E3/R7)-I1);
     I1];
     
C = inv(A)*B;