anchor.diff:        REAL*8 K1,K2,K3
         REAL*8 U2,V2,W2
         REAL*8 U3,V3,W3
  +      REAL*8 xx,xy,yy,dd,xd,xc,xq,yq,dq,pq
         INTEGER thru
   
         COMMON /SOURCE/ sd,cd,s2d,c2d,cdcd,sdsd,cdsd
  
positive.code:   404             continue
    405         continue
            else
                call rectxder(fx,ksi(ii),eta(jj),q,z)
                call rectyder(fy,ksi(ii),eta(jj),q,z)
                call rectzder(fz,ksi(ii),eta(jj),q,z)
                do 406 i = 1,6
                    fj(i,1) = fj(i,1) - fac*fx(i,1)
                    fk(i,1) = fk(i,1) - fac*fy(i,1)
  
negative.code: 
  C-------------------
  
        SUBROUTINE yderiv1(fy,ksi,eta,q,z)
  C----
  C Components of y-derivatives of displacement from finite source
  C----
  