anchor.diff:       |                             !xi(1) is e neutrino degeneracy parameter.
        |                             !xi(2) is m neutrino degeneracy parameter.
        |                             !xi(3) is t neutrino degeneracy parameter.
  +      REAL    b                    !Fierz parameter
   
   C----------DEFAULT VARIATIONAL PARAMETERS.
         REAL    dt0                  !Default initial time step.
  
positive.code:       COMMON /ttime/   t,dt,dlt9dt                   !Time variables.
        COMMON /thermcb/  thm,hubcst                   !Dynamic variables.
        COMMON /endens/ rhone0,rhob0,rhob,rnb          !Energy densities.
        COMMON /lncoef/ a,b,yx                         !Linear eqn coefficients.
        COMMON /nucdat/ am,zm,dm                       !Nuclide data.
        COMMON /besselcb/ bl1,bl2,bl3,bl4,bl5,           !Eval function bl(z).
       |                bm1,bm2,bm3,bm4,bm5,           !Eval function bm(z).
  
negative.code: 
  C----------MATRIX COEFFICIENTS FOR LINEAR EQUATION.
        DOUBLE PRECISION a(nnuc,nnuc)!Relates y(t+dt) to y(t).
        REAL    b_(nnuc)              !Contains y0 in inverse order.
        REAL    yx(nnuc)             !yy in reverse order.
  
  C----------NUCLIDE DATA.
  