source 2007 Feng--Wu, first JQN2 doubling formula, plus correction of obvious typos, plus epsilon=1, plus delta=-a, plus scaling, plus common-subexpression elimination compute A1 = (R1+2 Y1)^2 compute A2 = 4 Y1^2 compute Q1 = XX1^2 compute S1 = R1^2 compute S12 = 2 S1 compute M = a S12 compute A2M = A2-M compute X3 = A1-A2-S1 compute Y3 = A2M(A2+M)+S12^2 compute Z3 = A2M-8 Q1 compute XX3 = X3^2 compute ZZ3 = Z3^2 compute T3 = XX3+ZZ3 compute R3 = (X3+Z3)^2-T3