\[\left(\left(-2 \cdot J\right) \cdot \cos \left(\frac{K}{2}\right)\right) \cdot \sqrt{1 + {\left(\frac{U}{\left(2 \cdot J\right) \cdot \cos \left(\frac{K}{2}\right)}\right)}^{2}}\]

↓

\[\left(-2 \cdot \left(\cos \left(\frac{K}{2}\right) \cdot J\right)\right) \cdot \sqrt{1^2 + \left(\frac{U}{\left(\cos \left(\frac{K}{2}\right) \cdot J\right) \cdot 2}\right)^2}^*\]

Error

The X axis uses an exponential scale — Bits error versus `J`

Derivation

Initial program 17.5
\[\left(\left(-2 \cdot J\right) \cdot \cos \left(\frac{K}{2}\right)\right) \cdot \sqrt{1 + {\left(\frac{U}{\left(2 \cdot J\right) \cdot \cos \left(\frac{K}{2}\right)}\right)}^{2}}\]
Simplified7.8
\[\leadsto \color{blue}{\sqrt{1^2 + \left(\frac{U}{2 \cdot \left(\cos \left(\frac{K}{2}\right) \cdot J\right)}\right)^2}^* \cdot \left(-2 \cdot \left(\cos \left(\frac{K}{2}\right) \cdot J\right)\right)}\]
Final simplification7.8
\[\leadsto \left(-2 \cdot \left(\cos \left(\frac{K}{2}\right) \cdot J\right)\right) \cdot \sqrt{1^2 + \left(\frac{U}{\left(\cos \left(\frac{K}{2}\right) \cdot J\right) \cdot 2}\right)^2}^*\]

Reproduce

herbie shell --seed 2019089 +o rules:numerics
(FPCore (J K U)
  :name "Maksimov and Kolovsky, Equation (3)"
  (* (* (* -2 J) (cos (/ K 2))) (sqrt (+ 1 (pow (/ U (* (* 2 J) (cos (/ K 2)))) 2)))))