anchor.diff:  C   CODED BY I. M. IDRISS  1967
   C * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
   C
  +C     TODO: These arrays need to be checked for size
         dimension XD(2), XV(2), T(3)
         dimension UG(1)
   C
  
positive.code:       CIRE= A(2*I-1) + A(K6)
        CIIM=A(2*I)-A(K6+1)
        CNIRE=(-SI*(A(2*I)+A(K6+1))+CO*(A(2*I-1)-A(K6)))
        IF(SI)62,61,62
     62 CNIIM=(A(2*I-1)-A(K6)-CO*CNIRE)/SI
        go to 63
     61 CNIIM=0.
  
negative.code: C* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
        dimension A(1),INV(1),S(1),N(3),M(3),NP(3),W(2),W2(2),W3(2)
        EQUIVALENCE (N1,N(1)), (N2,N(2)), (N3,N(3))
  
        M1=M(1)
        M2=M(2)
        M3=M(3)
  