180 \cdot \frac{\tan^{-1} \left(\frac{\left(\frac{\frac{{\left(a \cdot \cos \left(\frac{angle}{180} \cdot \pi\right)\right)}^{2} + {\left(b \cdot \sin \left(\frac{angle}{180} \cdot \pi\right)\right)}^{2}}{y-scale}}{y-scale} - \frac{\frac{{\left(a \cdot \sin \left(\frac{angle}{180} \cdot \pi\right)\right)}^{2} + {\left(b \cdot \cos \left(\frac{angle}{180} \cdot \pi\right)\right)}^{2}}{x-scale}}{x-scale}\right) - \sqrt{{\left(\frac{\frac{{\left(a \cdot \sin \left(\frac{angle}{180} \cdot \pi\right)\right)}^{2} + {\left(b \cdot \cos \left(\frac{angle}{180} \cdot \pi\right)\right)}^{2}}{x-scale}}{x-scale} - \frac{\frac{{\left(a \cdot \cos \left(\frac{angle}{180} \cdot \pi\right)\right)}^{2} + {\left(b \cdot \sin \left(\frac{angle}{180} \cdot \pi\right)\right)}^{2}}{y-scale}}{y-scale}\right)}^{2} + {\left(\frac{\frac{\left(\left(2 \cdot \left({b}^{2} - {a}^{2}\right)\right) \cdot \sin \left(\frac{angle}{180} \cdot \pi\right)\right) \cdot \cos \left(\frac{angle}{180} \cdot \pi\right)}{x-scale}}{y-scale}\right)}^{2}}}{\frac{\frac{\left(\left(2 \cdot \left({b}^{2} - {a}^{2}\right)\right) \cdot \sin \left(\frac{angle}{180} \cdot \pi\right)\right) \cdot \cos \left(\frac{angle}{180} \cdot \pi\right)}{x-scale}}{y-scale}}\right)}{\pi}
\begin{array}{l}
t_0 := \frac{angle}{180} \cdot \pi\\
t_1 := \cos t_0\\
t_2 := \sin t_0\\
t_3 := \frac{\frac{t_1 \cdot \left(t_2 \cdot \left(2 \cdot \left({b}^{2} - {a}^{2}\right)\right)\right)}{x-scale}}{y-scale}\\
t_4 := {\left(b \cdot t_2\right)}^{2}\\
t_5 := {\left(a \cdot t_2\right)}^{2}\\
180 \cdot \frac{\tan^{-1} \left(\frac{\left(\frac{\frac{{\left(a \cdot t_1\right)}^{2} + t_4}{y-scale}}{y-scale} - \frac{\frac{t_5 + {\left(b \cdot \left(1 - 1.54320987654321 \cdot 10^{-5} \cdot {\left(angle \cdot \pi\right)}^{2}\right)\right)}^{2}}{x-scale}}{x-scale}\right) - \sqrt{{\left(\frac{\frac{t_5 + {\left(t_1 \cdot b\right)}^{2}}{x-scale}}{x-scale} - \frac{\frac{t_4 + {a}^{2}}{y-scale}}{y-scale}\right)}^{2} + {t_3}^{2}}}{t_3}\right)}{\pi}
\end{array}
(FPCore (a b angle x-scale y-scale)
:precision binary64
(*
180.0
(/
(atan
(/
(-
(-
(/
(/
(+
(pow (* a (cos (* (/ angle 180.0) PI))) 2.0)
(pow (* b (sin (* (/ angle 180.0) PI))) 2.0))
y-scale)
y-scale)
(/
(/
(+
(pow (* a (sin (* (/ angle 180.0) PI))) 2.0)
(pow (* b (cos (* (/ angle 180.0) PI))) 2.0))
x-scale)
x-scale))
(sqrt
(+
(pow
(-
(/
(/
(+
(pow (* a (sin (* (/ angle 180.0) PI))) 2.0)
(pow (* b (cos (* (/ angle 180.0) PI))) 2.0))
x-scale)
x-scale)
(/
(/
(+
(pow (* a (cos (* (/ angle 180.0) PI))) 2.0)
(pow (* b (sin (* (/ angle 180.0) PI))) 2.0))
y-scale)
y-scale))
2.0)
(pow
(/
(/
(*
(*
(* 2.0 (- (pow b 2.0) (pow a 2.0)))
(sin (* (/ angle 180.0) PI)))
(cos (* (/ angle 180.0) PI)))
x-scale)
y-scale)
2.0))))
(/
(/
(*
(* (* 2.0 (- (pow b 2.0) (pow a 2.0))) (sin (* (/ angle 180.0) PI)))
(cos (* (/ angle 180.0) PI)))
x-scale)
y-scale)))
PI)))(FPCore (a b angle x-scale y-scale)
:precision binary64
(let* ((t_0 (* (/ angle 180.0) PI))
(t_1 (cos t_0))
(t_2 (sin t_0))
(t_3
(/
(/ (* t_1 (* t_2 (* 2.0 (- (pow b 2.0) (pow a 2.0))))) x-scale)
y-scale))
(t_4 (pow (* b t_2) 2.0))
(t_5 (pow (* a t_2) 2.0)))
(*
180.0
(/
(atan
(/
(-
(-
(/ (/ (+ (pow (* a t_1) 2.0) t_4) y-scale) y-scale)
(/
(/
(+
t_5
(pow
(* b (- 1.0 (* 1.54320987654321e-5 (pow (* angle PI) 2.0))))
2.0))
x-scale)
x-scale))
(sqrt
(+
(pow
(-
(/ (/ (+ t_5 (pow (* t_1 b) 2.0)) x-scale) x-scale)
(/ (/ (+ t_4 (pow a 2.0)) y-scale) y-scale))
2.0)
(pow t_3 2.0))))
t_3))
PI))))double code(double a, double b, double angle, double x_45_scale, double y_45_scale) {
return 180.0 * (atan((((((pow((a * cos((angle / 180.0) * ((double) M_PI))), 2.0) + pow((b * sin((angle / 180.0) * ((double) M_PI))), 2.0)) / y_45_scale) / y_45_scale) - (((pow((a * sin((angle / 180.0) * ((double) M_PI))), 2.0) + pow((b * cos((angle / 180.0) * ((double) M_PI))), 2.0)) / x_45_scale) / x_45_scale)) - sqrt(pow(((((pow((a * sin((angle / 180.0) * ((double) M_PI))), 2.0) + pow((b * cos((angle / 180.0) * ((double) M_PI))), 2.0)) / x_45_scale) / x_45_scale) - (((pow((a * cos((angle / 180.0) * ((double) M_PI))), 2.0) + pow((b * sin((angle / 180.0) * ((double) M_PI))), 2.0)) / y_45_scale) / y_45_scale)), 2.0) + pow((((((2.0 * (pow(b, 2.0) - pow(a, 2.0))) * sin((angle / 180.0) * ((double) M_PI))) * cos((angle / 180.0) * ((double) M_PI))) / x_45_scale) / y_45_scale), 2.0))) / (((((2.0 * (pow(b, 2.0) - pow(a, 2.0))) * sin((angle / 180.0) * ((double) M_PI))) * cos((angle / 180.0) * ((double) M_PI))) / x_45_scale) / y_45_scale)) / ((double) M_PI));
}
double code(double a, double b, double angle, double x_45_scale, double y_45_scale) {
double t_0 = (angle / 180.0) * ((double) M_PI);
double t_1 = cos(t_0);
double t_2 = sin(t_0);
double t_3 = ((t_1 * (t_2 * (2.0 * (pow(b, 2.0) - pow(a, 2.0))))) / x_45_scale) / y_45_scale;
double t_4 = pow((b * t_2), 2.0);
double t_5 = pow((a * t_2), 2.0);
return 180.0 * (atan((((((pow((a * t_1), 2.0) + t_4) / y_45_scale) / y_45_scale) - (((t_5 + pow((b * (1.0 - (1.54320987654321e-5 * pow((angle * ((double) M_PI)), 2.0)))), 2.0)) / x_45_scale) / x_45_scale)) - sqrt(pow(((((t_5 + pow((t_1 * b), 2.0)) / x_45_scale) / x_45_scale) - (((t_4 + pow(a, 2.0)) / y_45_scale) / y_45_scale)), 2.0) + pow(t_3, 2.0))) / t_3) / ((double) M_PI));
}



Bits error versus a



Bits error versus b



Bits error versus angle



Bits error versus x-scale



Bits error versus y-scale
Results
Initial program 55.0
Taylor expanded around 0 54.3
Simplified54.3
Taylor expanded around 0 54.3
Final simplification54.3
herbie shell --seed 2021198
(FPCore (a b angle x-scale y-scale)
:name "raw-angle from scale-rotated-ellipse"
:precision binary64
(* 180.0 (/ (atan (/ (- (- (/ (/ (+ (pow (* a (cos (* (/ angle 180.0) PI))) 2.0) (pow (* b (sin (* (/ angle 180.0) PI))) 2.0)) y-scale) y-scale) (/ (/ (+ (pow (* a (sin (* (/ angle 180.0) PI))) 2.0) (pow (* b (cos (* (/ angle 180.0) PI))) 2.0)) x-scale) x-scale)) (sqrt (+ (pow (- (/ (/ (+ (pow (* a (sin (* (/ angle 180.0) PI))) 2.0) (pow (* b (cos (* (/ angle 180.0) PI))) 2.0)) x-scale) x-scale) (/ (/ (+ (pow (* a (cos (* (/ angle 180.0) PI))) 2.0) (pow (* b (sin (* (/ angle 180.0) PI))) 2.0)) y-scale) y-scale)) 2.0) (pow (/ (/ (* (* (* 2.0 (- (pow b 2.0) (pow a 2.0))) (sin (* (/ angle 180.0) PI))) (cos (* (/ angle 180.0) PI))) x-scale) y-scale) 2.0)))) (/ (/ (* (* (* 2.0 (- (pow b 2.0) (pow a 2.0))) (sin (* (/ angle 180.0) PI))) (cos (* (/ angle 180.0) PI))) x-scale) y-scale))) PI)))