anchor.diff:  
   C----------COMMON AREAS.
         COMMON /compr/  cy,ct,t9i,t9f,ytmin,inc        !Computation parameters.
  -      COMMON /lncoef/ a,b_,y                          !Lin eqn coefficients. 
  +      COMMON /lncoef/ a,bkevin,y                     !Lin eqn coefficients. 
         COMMON /flags/  ltime,is,ip,it,mbad            !Flags, counters.
         COMMON /runopt/ irun,isize,jsize               !Run options.
   
  
positive.code:           END IF
          END DO
          a(i,i) = 1.d0 + a(i,i)     !Add identity matrix to a-matrix.
          b_(i1)  = y0(i)             !Initial abundances.
        END DO
  
  C50--------SOLVE EQUATIONS TO GET DERIVATIVE------------------------------------
  
negative.code: 
  C----------COMPONENTS OF MATRIX EQUATION.
        DOUBLE PRECISION a(nnuc,nnuc)!Relates y(t-dt) to y(t).
        REAL    bkevin(nnuc)         !Contains y0 in inverse order.
        REAL    yx(nnuc)             !yy in reverse order.
  
  C----------COUNTERS AND FLAGS.
  