This is a known bug, related to some recent change in the treatment of derivatives of symbolic functions, cf. this discussion. In your case, the bug shows up because of both G[1,1]=diff(f(R),R) and the square root in S[1,1]=R^(0.5).
This is a known bug, related to some recent change in the treatment of derivatives of symbolic functions, cf. this discussion. In your case, the bug shows up because of both G[1,1]=diff(f(R),R) and the square root in S[1,1]=R^(0.5).