anchor.diff:                  zero_value = zero_value*zero_value
                ELSE
                   tempfx = (zero_value*zero_value) &
  -                         & * (4.0_NTREAL*zero_value - 3.0_NTREAL*zero_value*zero_value)
  +                     & * (4.0_NTREAL*zero_value - &
  +                     & 3.0_NTREAL*zero_value*zero_value)
                   tempgx = (zero_value*zero_value) * (1.0_NTREAL-zero_value) &
  -                         & * (0.0_NTREAL-zero_value)
  +                     & * (0.0_NTREAL-zero_value)
                   zero_value = tempfx + sigma_array(inner_counter)*tempgx
                END IF
             END DO polynomial
  
positive.code:           zero_value = midpoint
            !! Compute polynomial function at the guess point.
            polynomial:DO inner_counter=1,total_iterations
               zero_value = zero_value + 2.0_NTREAL*((zero_value*zero_value)*(1.0_NTREAL-zero_value) &
                            & - sigma_array(inner_counter)*(zero_value*(1.0_NTREAL-zero_value)))
            END DO polynomial
            !! Change bracketing.
            IF (zero_value .LT. 0.5_NTREAL) THEN
  
negative.code:              interval_b = midpoint
            END IF
            !! Check convergence.
            IF (ABS(zero_value-0.5_NTREAL) .LT. &
                 & solver_parameters%converge_diff) THEN
               EXIT
            END IF
         END DO midpoints
  