Error

Target

Derivation

1. Split input into 2 regimes

2. if a < 1.2074200159435737e+229

   1. Initial program 59.1

      \[\frac{\varepsilon \cdot \left(e^{\left(a + b\right) \cdot \varepsilon} - 1\right)}{\left(e^{a \cdot \varepsilon} - 1\right) \cdot \left(e^{b \cdot \varepsilon} - 1\right)}\]

   2. Simplified35.1

      \[\leadsto \color{blue}{\frac{\frac{(e^{\left(a + b\right) \cdot \varepsilon} - 1)^* \cdot \varepsilon}{(e^{\varepsilon \cdot a} - 1)^*}}{(e^{\varepsilon \cdot b} - 1)^*}}\]

   3. Taylor expanded around 0 2.9

      \[\leadsto \color{blue}{\frac{1}{a} + \frac{1}{b}}\]

   if 1.2074200159435737e+229 < a

   1. Initial program 49.0

      \[\frac{\varepsilon \cdot \left(e^{\left(a + b\right) \cdot \varepsilon} - 1\right)}{\left(e^{a \cdot \varepsilon} - 1\right) \cdot \left(e^{b \cdot \varepsilon} - 1\right)}\]

   2. Simplified18.4

      \[\leadsto \color{blue}{\frac{\frac{(e^{\left(a + b\right) \cdot \varepsilon} - 1)^* \cdot \varepsilon}{(e^{\varepsilon \cdot a} - 1)^*}}{(e^{\varepsilon \cdot b} - 1)^*}}\]
   3. Using strategy rm

   4. Applied clear-num18.4

      \[\leadsto \color{blue}{\frac{1}{\frac{(e^{\varepsilon \cdot b} - 1)^*}{\frac{(e^{\left(a + b\right) \cdot \varepsilon} - 1)^* \cdot \varepsilon}{(e^{\varepsilon \cdot a} - 1)^*}}}}\]
3. Recombined 2 regimes into one program.

4. Final simplification3.6

   \[\leadsto \begin{array}{l} \mathbf{if}\;a \le 1.2074200159435737 \cdot 10^{+229}:\\ \;\;\;\;\frac{1}{b} + \frac{1}{a}\\ \mathbf{else}:\\ \;\;\;\;\frac{1}{\frac{(e^{\varepsilon \cdot b} - 1)^*}{\frac{(e^{\left(b + a\right) \cdot \varepsilon} - 1)^* \cdot \varepsilon}{(e^{a \cdot \varepsilon} - 1)^*}}}\\ \end{array}\]

Reproduce

herbie shell --seed 2019100 +o rules:numerics
(FPCore (a b eps)
  :name "expq3 (problem 3.4.2)"
  :pre (and (< -1 eps) (< eps 1))

  :herbie-target
  (/ (+ a b) (* a b))

  (/ (* eps (- (exp (* (+ a b) eps)) 1)) (* (- (exp (* a eps)) 1) (- (exp (* b eps)) 1))))