anchor.diff:  
   C----------COMPONENTS OF MATRIX EQUATION.
         DOUBLE PRECISION a(nnuc,nnuc)!Relates y(t-dt) to y(t).
  -      REAL    b(nnuc)              !Contains y0 in inverse order.
  +      REAL    b_(nnuc)              !Contains y0 in inverse order.
         REAL    yx(nnuc)             !yy in reverse order.
   
   C----------COUNTERS AND FLAGS.
  
positive.code:         part1 = 1./(1.+ex(-.511*x/t9mev))
          part2 = 1./(1.+ex(+(x-2.531)*(.511/tnmev)-xi(1)))
  C       func1 = cnorm*x*(x-2.531)**2*(x**2-1)**.5*part1*part2
        IF (x.gt.(2.531) THEN
          func1 = cnorm*(x+b*.511)*(x-2.531)**2*(x**2-1)**.5*part1*part2
        ELSE
          func1 = cnorm*(x-b*.511)*(x-2.531)**2*(x**2-1)**.5*part1*part2
        END IF
        END IF
        RETURN
        end
  
negative.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------------------------------------
  