/* Useful Test vectors for a, b, c, d for f(x) = ax^3 + bx^2 + cx + d.
        1 0 -1 0 ;                -1 (min), 1 (max) 
        1 1 0 1 ;                 -1.4656 (outside bounds)
        1 0 -0.5 0 ;              -0.707 (- to +), 0 (+ to -), 0.707
        1 -0.8 1 -0.8 ;           0.8 (- to +)
        1 -0.11 1 -0.11 ;         0.11 (- to +)
        1 -1 1 -1 ;               1 (max, - to +)
        1 -8 1 5 ;                -0.702 (- to +), 0.913, 7.79 (outside)
        -1 2 0 -0.9 ;             -0.5895 (+ to -), 0.9077, 1.68 (outside)
        -1 4 0 -1 ;               -0.47283 (+ to -), 0.53740, 3.9354 (outside)
        0 1 -0.9 0.2025 ;         0.45 (bounce, quadratic function)
        -1 -0.6 0.0675 0.06075 ;  -0.45 (bounce), 0.3 (+ to -)
        1 -0.6 -0.0675 0.06075 ;  -0.3 (- to +), 0.45 (bounce)
        4 5 -1 -2 ;               -1 (min, - to +), -0.84307, 0.59307
        1 1 9 1 ;                 -0.11236 (- to +)
        1 0.996 0 0 ;             -0.996, 0 (bounce)
      */