Ri+R2 R3 g13+g2-g R3 R2+R g12g2+g23 Ri+ r R g13+g12 g12 10 R3 R2+ R g12g12+g = 等效条件 rir2 r12731 r12=R1+R2+ R R3 2+23+r31 R2R R2+R3+ 12723 R r2 r12+23+3 R3R r31=R3+R1+ 23/31 r2 R r12+23+733 2 3 1 2 3 R R R R R R + + -1 12 12 23 13 12 12 g g g g g g − + + − = 3 2 3 1 2 3 R R R R R R + + 12 12 23 13 12 12 g g g g g g − + + − = 0 1 1 0 3 1 2 12 1 2 R R R r = R + R + 1 2 3 23 2 3 R R R r = R + R + 2 3 1 31 3 1 R R R r = R + R + 12 23 31 12 31 1 r r r r r R + + = 12 23 31 12 23 2 r r r r r R + + = 12 23 31 23 31 3 r r r r r R + + = 等效条件