\[\frac{\left(-b/2\right) + \sqrt{{b/2}^2 - a \cdot c}}{a}\]
Test:
NMSE problem 3.2.1, positive
Bits:
128 bits
Bits error versus a
Bits error versus b/2
Bits error versus c
Time: 11.3 s
Input Error: 19.1
Output Error: 3.3
Log: ⚲
Profile: 🕒
\(\begin{cases} \frac{\frac{1}{2}}{\frac{b/2}{c}} - \frac{b/2}{a} \cdot 2 & \text{when } b/2 \le -1.0189882f+17 \\ \frac{\left(-b/2\right) + \sqrt{{b/2}^2 - a \cdot c}}{a} & \text{when } b/2 \le 3.3176054f-21 \\ \frac{c}{(\left(a \cdot \frac{1}{2}\right) * \left(\frac{c}{b/2}\right) + \left(-b/2\right))_* - b/2} & \text{otherwise} \end{cases}\)

    if b/2 < -1.0189882f+17

    1. Started with
      \[\frac{\left(-b/2\right) + \sqrt{{b/2}^2 - a \cdot c}}{a}\]
      25.4
    2. Applied taylor to get
      \[\frac{\left(-b/2\right) + \sqrt{{b/2}^2 - a \cdot c}}{a} \leadsto \frac{\frac{1}{2} \cdot \frac{c \cdot a}{b/2} - 2 \cdot b/2}{a}\]
      6.2
    3. Taylor expanded around -inf to get
      \[\frac{\color{red}{\frac{1}{2} \cdot \frac{c \cdot a}{b/2} - 2 \cdot b/2}}{a} \leadsto \frac{\color{blue}{\frac{1}{2} \cdot \frac{c \cdot a}{b/2} - 2 \cdot b/2}}{a}\]
      6.2
    4. Applied simplify to get
      \[\color{red}{\frac{\frac{1}{2} \cdot \frac{c \cdot a}{b/2} - 2 \cdot b/2}{a}} \leadsto \color{blue}{\frac{\frac{1}{2}}{\frac{b/2}{c}} - \frac{b/2}{a} \cdot 2}\]
      0.0

    if -1.0189882f+17 < b/2 < 3.3176054f-21

    1. Started with
      \[\frac{\left(-b/2\right) + \sqrt{{b/2}^2 - a \cdot c}}{a}\]
      4.7

    if 3.3176054f-21 < b/2

    1. Started with
      \[\frac{\left(-b/2\right) + \sqrt{{b/2}^2 - a \cdot c}}{a}\]
      28.2
    2. Using strategy rm
      28.2
    3. Applied flip-+ to get
      \[\frac{\color{red}{\left(-b/2\right) + \sqrt{{b/2}^2 - a \cdot c}}}{a} \leadsto \frac{\color{blue}{\frac{{\left(-b/2\right)}^2 - {\left(\sqrt{{b/2}^2 - a \cdot c}\right)}^2}{\left(-b/2\right) - \sqrt{{b/2}^2 - a \cdot c}}}}{a}\]
      29.4
    4. Applied simplify to get
      \[\frac{\frac{\color{red}{{\left(-b/2\right)}^2 - {\left(\sqrt{{b/2}^2 - a \cdot c}\right)}^2}}{\left(-b/2\right) - \sqrt{{b/2}^2 - a \cdot c}}}{a} \leadsto \frac{\frac{\color{blue}{a \cdot c}}{\left(-b/2\right) - \sqrt{{b/2}^2 - a \cdot c}}}{a}\]
      18.2
    5. Using strategy rm
      18.2
    6. Applied add-exp-log to get
      \[\frac{\frac{a \cdot c}{\left(-b/2\right) - \color{red}{\sqrt{{b/2}^2 - a \cdot c}}}}{a} \leadsto \frac{\frac{a \cdot c}{\left(-b/2\right) - \color{blue}{e^{\log \left(\sqrt{{b/2}^2 - a \cdot c}\right)}}}}{a}\]
      18.4
    7. Applied taylor to get
      \[\frac{\frac{a \cdot c}{\left(-b/2\right) - e^{\log \left(\sqrt{{b/2}^2 - a \cdot c}\right)}}}{a} \leadsto \frac{\frac{a \cdot c}{\left(-b/2\right) - e^{\log \left(b/2 - \frac{1}{2} \cdot \frac{c \cdot a}{b/2}\right)}}}{a}\]
      11.0
    8. Taylor expanded around inf to get
      \[\frac{\frac{a \cdot c}{\left(-b/2\right) - e^{\log \color{red}{\left(b/2 - \frac{1}{2} \cdot \frac{c \cdot a}{b/2}\right)}}}}{a} \leadsto \frac{\frac{a \cdot c}{\left(-b/2\right) - e^{\log \color{blue}{\left(b/2 - \frac{1}{2} \cdot \frac{c \cdot a}{b/2}\right)}}}}{a}\]
      11.0
    9. Applied simplify to get
      \[\color{red}{\frac{\frac{a \cdot c}{\left(-b/2\right) - e^{\log \left(b/2 - \frac{1}{2} \cdot \frac{c \cdot a}{b/2}\right)}}}{a}} \leadsto \color{blue}{\frac{c}{(\left(a \cdot \frac{1}{2}\right) * \left(\frac{c}{b/2}\right) + \left(-b/2\right))_* - b/2}}\]
      3.0
  1. Removed slow pow expressions

Original test:


(lambda ((a default) (b/2 default) (c default))
  #:name "NMSE problem 3.2.1, positive"
  (/ (+ (- b/2) (sqrt (- (sqr b/2) (* a c)))) a))