Quotient of products

Percentage Accurate: 86.5% → 97.9%
Time: 3.3s
Alternatives: 3
Speedup: 1.0×

Specification

?
\[\begin{array}{l} \\ \frac{a1 \cdot a2}{b1 \cdot b2} \end{array} \]
(FPCore (a1 a2 b1 b2) :precision binary64 (/ (* a1 a2) (* b1 b2)))
double code(double a1, double a2, double b1, double b2) {
	return (a1 * a2) / (b1 * b2);
}
real(8) function code(a1, a2, b1, b2)
    real(8), intent (in) :: a1
    real(8), intent (in) :: a2
    real(8), intent (in) :: b1
    real(8), intent (in) :: b2
    code = (a1 * a2) / (b1 * b2)
end function
public static double code(double a1, double a2, double b1, double b2) {
	return (a1 * a2) / (b1 * b2);
}
def code(a1, a2, b1, b2):
	return (a1 * a2) / (b1 * b2)
function code(a1, a2, b1, b2)
	return Float64(Float64(a1 * a2) / Float64(b1 * b2))
end
function tmp = code(a1, a2, b1, b2)
	tmp = (a1 * a2) / (b1 * b2);
end
code[a1_, a2_, b1_, b2_] := N[(N[(a1 * a2), $MachinePrecision] / N[(b1 * b2), $MachinePrecision]), $MachinePrecision]
\begin{array}{l}

\\
\frac{a1 \cdot a2}{b1 \cdot b2}
\end{array}

Sampling outcomes in binary64 precision:

Local Percentage Accuracy vs ?

The average percentage accuracy by input value. Horizontal axis shows value of an input variable; the variable is choosen in the title. Vertical axis is accuracy; higher is better. Red represent the original program, while blue represents Herbie's suggestion. These can be toggled with buttons below the plot. The line is an average while dots represent individual samples.

Accuracy vs Speed?

Herbie found 3 alternatives:

AlternativeAccuracySpeedup
The accuracy (vertical axis) and speed (horizontal axis) of each alternatives. Up and to the right is better. The red square shows the initial program, and each blue circle shows an alternative.The line shows the best available speed-accuracy tradeoffs.

Initial Program: 86.5% accurate, 1.0× speedup?

\[\begin{array}{l} \\ \frac{a1 \cdot a2}{b1 \cdot b2} \end{array} \]
(FPCore (a1 a2 b1 b2) :precision binary64 (/ (* a1 a2) (* b1 b2)))
double code(double a1, double a2, double b1, double b2) {
	return (a1 * a2) / (b1 * b2);
}
real(8) function code(a1, a2, b1, b2)
    real(8), intent (in) :: a1
    real(8), intent (in) :: a2
    real(8), intent (in) :: b1
    real(8), intent (in) :: b2
    code = (a1 * a2) / (b1 * b2)
end function
public static double code(double a1, double a2, double b1, double b2) {
	return (a1 * a2) / (b1 * b2);
}
def code(a1, a2, b1, b2):
	return (a1 * a2) / (b1 * b2)
function code(a1, a2, b1, b2)
	return Float64(Float64(a1 * a2) / Float64(b1 * b2))
end
function tmp = code(a1, a2, b1, b2)
	tmp = (a1 * a2) / (b1 * b2);
end
code[a1_, a2_, b1_, b2_] := N[(N[(a1 * a2), $MachinePrecision] / N[(b1 * b2), $MachinePrecision]), $MachinePrecision]
\begin{array}{l}

\\
\frac{a1 \cdot a2}{b1 \cdot b2}
\end{array}

Alternative 1: 97.9% accurate, 0.8× speedup?

\[\begin{array}{l} b2\_m = \left|b2\right| \\ b2\_s = \mathsf{copysign}\left(1, b2\right) \\ b1\_m = \left|b1\right| \\ b1\_s = \mathsf{copysign}\left(1, b1\right) \\ a2\_m = \left|a2\right| \\ a2\_s = \mathsf{copysign}\left(1, a2\right) \\ a1\_m = \left|a1\right| \\ a1\_s = \mathsf{copysign}\left(1, a1\right) \\ [a1_m, a2_m, b1_m, b2_m] = \mathsf{sort}([a1_m, a2_m, b1_m, b2_m])\\\\ [a1_m, a2_m, b1_m, b2_m] = \mathsf{sort}([a1_m, a2_m, b1_m, b2_m])\\ \\ a1\_s \cdot \left(a2\_s \cdot \left(b1\_s \cdot \left(b2\_s \cdot \left(\frac{a1\_m}{b1\_m} \cdot \frac{a2\_m}{b2\_m}\right)\right)\right)\right) \end{array} \]
b2\_m = (fabs.f64 b2)
b2\_s = (copysign.f64 #s(literal 1 binary64) b2)
b1\_m = (fabs.f64 b1)
b1\_s = (copysign.f64 #s(literal 1 binary64) b1)
a2\_m = (fabs.f64 a2)
a2\_s = (copysign.f64 #s(literal 1 binary64) a2)
a1\_m = (fabs.f64 a1)
a1\_s = (copysign.f64 #s(literal 1 binary64) a1)
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
(FPCore (a1_s a2_s b1_s b2_s a1_m a2_m b1_m b2_m)
 :precision binary64
 (* a1_s (* a2_s (* b1_s (* b2_s (* (/ a1_m b1_m) (/ a2_m b2_m)))))))
b2\_m = fabs(b2);
b2\_s = copysign(1.0, b2);
b1\_m = fabs(b1);
b1\_s = copysign(1.0, b1);
a2\_m = fabs(a2);
a2\_s = copysign(1.0, a2);
a1\_m = fabs(a1);
a1\_s = copysign(1.0, a1);
assert(a1_m < a2_m && a2_m < b1_m && b1_m < b2_m);
assert(a1_m < a2_m && a2_m < b1_m && b1_m < b2_m);
double code(double a1_s, double a2_s, double b1_s, double b2_s, double a1_m, double a2_m, double b1_m, double b2_m) {
	return a1_s * (a2_s * (b1_s * (b2_s * ((a1_m / b1_m) * (a2_m / b2_m)))));
}
b2\_m = abs(b2)
b2\_s = copysign(1.0d0, b2)
b1\_m = abs(b1)
b1\_s = copysign(1.0d0, b1)
a2\_m = abs(a2)
a2\_s = copysign(1.0d0, a2)
a1\_m = abs(a1)
a1\_s = copysign(1.0d0, a1)
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
real(8) function code(a1_s, a2_s, b1_s, b2_s, a1_m, a2_m, b1_m, b2_m)
    real(8), intent (in) :: a1_s
    real(8), intent (in) :: a2_s
    real(8), intent (in) :: b1_s
    real(8), intent (in) :: b2_s
    real(8), intent (in) :: a1_m
    real(8), intent (in) :: a2_m
    real(8), intent (in) :: b1_m
    real(8), intent (in) :: b2_m
    code = a1_s * (a2_s * (b1_s * (b2_s * ((a1_m / b1_m) * (a2_m / b2_m)))))
end function
b2\_m = Math.abs(b2);
b2\_s = Math.copySign(1.0, b2);
b1\_m = Math.abs(b1);
b1\_s = Math.copySign(1.0, b1);
a2\_m = Math.abs(a2);
a2\_s = Math.copySign(1.0, a2);
a1\_m = Math.abs(a1);
a1\_s = Math.copySign(1.0, a1);
assert a1_m < a2_m && a2_m < b1_m && b1_m < b2_m;
assert a1_m < a2_m && a2_m < b1_m && b1_m < b2_m;
public static double code(double a1_s, double a2_s, double b1_s, double b2_s, double a1_m, double a2_m, double b1_m, double b2_m) {
	return a1_s * (a2_s * (b1_s * (b2_s * ((a1_m / b1_m) * (a2_m / b2_m)))));
}
b2\_m = math.fabs(b2)
b2\_s = math.copysign(1.0, b2)
b1\_m = math.fabs(b1)
b1\_s = math.copysign(1.0, b1)
a2\_m = math.fabs(a2)
a2\_s = math.copysign(1.0, a2)
a1\_m = math.fabs(a1)
a1\_s = math.copysign(1.0, a1)
[a1_m, a2_m, b1_m, b2_m] = sort([a1_m, a2_m, b1_m, b2_m])
[a1_m, a2_m, b1_m, b2_m] = sort([a1_m, a2_m, b1_m, b2_m])
def code(a1_s, a2_s, b1_s, b2_s, a1_m, a2_m, b1_m, b2_m):
	return a1_s * (a2_s * (b1_s * (b2_s * ((a1_m / b1_m) * (a2_m / b2_m)))))
b2\_m = abs(b2)
b2\_s = copysign(1.0, b2)
b1\_m = abs(b1)
b1\_s = copysign(1.0, b1)
a2\_m = abs(a2)
a2\_s = copysign(1.0, a2)
a1\_m = abs(a1)
a1\_s = copysign(1.0, a1)
a1_m, a2_m, b1_m, b2_m = sort([a1_m, a2_m, b1_m, b2_m])
a1_m, a2_m, b1_m, b2_m = sort([a1_m, a2_m, b1_m, b2_m])
function code(a1_s, a2_s, b1_s, b2_s, a1_m, a2_m, b1_m, b2_m)
	return Float64(a1_s * Float64(a2_s * Float64(b1_s * Float64(b2_s * Float64(Float64(a1_m / b1_m) * Float64(a2_m / b2_m))))))
end
b2\_m = abs(b2);
b2\_s = sign(b2) * abs(1.0);
b1\_m = abs(b1);
b1\_s = sign(b1) * abs(1.0);
a2\_m = abs(a2);
a2\_s = sign(a2) * abs(1.0);
a1\_m = abs(a1);
a1\_s = sign(a1) * abs(1.0);
a1_m, a2_m, b1_m, b2_m = num2cell(sort([a1_m, a2_m, b1_m, b2_m])){:}
a1_m, a2_m, b1_m, b2_m = num2cell(sort([a1_m, a2_m, b1_m, b2_m])){:}
function tmp = code(a1_s, a2_s, b1_s, b2_s, a1_m, a2_m, b1_m, b2_m)
	tmp = a1_s * (a2_s * (b1_s * (b2_s * ((a1_m / b1_m) * (a2_m / b2_m)))));
end
b2\_m = N[Abs[b2], $MachinePrecision]
b2\_s = N[With[{TMP1 = Abs[1.0], TMP2 = Sign[b2]}, TMP1 * If[TMP2 == 0, 1, TMP2]], $MachinePrecision]
b1\_m = N[Abs[b1], $MachinePrecision]
b1\_s = N[With[{TMP1 = Abs[1.0], TMP2 = Sign[b1]}, TMP1 * If[TMP2 == 0, 1, TMP2]], $MachinePrecision]
a2\_m = N[Abs[a2], $MachinePrecision]
a2\_s = N[With[{TMP1 = Abs[1.0], TMP2 = Sign[a2]}, TMP1 * If[TMP2 == 0, 1, TMP2]], $MachinePrecision]
a1\_m = N[Abs[a1], $MachinePrecision]
a1\_s = N[With[{TMP1 = Abs[1.0], TMP2 = Sign[a1]}, TMP1 * If[TMP2 == 0, 1, TMP2]], $MachinePrecision]
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
code[a1$95$s_, a2$95$s_, b1$95$s_, b2$95$s_, a1$95$m_, a2$95$m_, b1$95$m_, b2$95$m_] := N[(a1$95$s * N[(a2$95$s * N[(b1$95$s * N[(b2$95$s * N[(N[(a1$95$m / b1$95$m), $MachinePrecision] * N[(a2$95$m / b2$95$m), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]
\begin{array}{l}
b2\_m = \left|b2\right|
\\
b2\_s = \mathsf{copysign}\left(1, b2\right)
\\
b1\_m = \left|b1\right|
\\
b1\_s = \mathsf{copysign}\left(1, b1\right)
\\
a2\_m = \left|a2\right|
\\
a2\_s = \mathsf{copysign}\left(1, a2\right)
\\
a1\_m = \left|a1\right|
\\
a1\_s = \mathsf{copysign}\left(1, a1\right)
\\
[a1_m, a2_m, b1_m, b2_m] = \mathsf{sort}([a1_m, a2_m, b1_m, b2_m])\\\\
[a1_m, a2_m, b1_m, b2_m] = \mathsf{sort}([a1_m, a2_m, b1_m, b2_m])\\
\\
a1\_s \cdot \left(a2\_s \cdot \left(b1\_s \cdot \left(b2\_s \cdot \left(\frac{a1\_m}{b1\_m} \cdot \frac{a2\_m}{b2\_m}\right)\right)\right)\right)
\end{array}
Derivation
  1. Initial program 86.8%

    \[\frac{a1 \cdot a2}{b1 \cdot b2} \]
  2. Add Preprocessing
  3. Step-by-step derivation
    1. lift-/.f64N/A

      \[\leadsto \color{blue}{\frac{a1 \cdot a2}{b1 \cdot b2}} \]
    2. lift-*.f64N/A

      \[\leadsto \frac{\color{blue}{a1 \cdot a2}}{b1 \cdot b2} \]
    3. lift-*.f64N/A

      \[\leadsto \frac{a1 \cdot a2}{\color{blue}{b1 \cdot b2}} \]
    4. times-fracN/A

      \[\leadsto \color{blue}{\frac{a1}{b1} \cdot \frac{a2}{b2}} \]
    5. *-commutativeN/A

      \[\leadsto \color{blue}{\frac{a2}{b2} \cdot \frac{a1}{b1}} \]
    6. lower-*.f64N/A

      \[\leadsto \color{blue}{\frac{a2}{b2} \cdot \frac{a1}{b1}} \]
    7. lower-/.f64N/A

      \[\leadsto \color{blue}{\frac{a2}{b2}} \cdot \frac{a1}{b1} \]
    8. lower-/.f6485.0

      \[\leadsto \frac{a2}{b2} \cdot \color{blue}{\frac{a1}{b1}} \]
  4. Applied rewrites85.0%

    \[\leadsto \color{blue}{\frac{a2}{b2} \cdot \frac{a1}{b1}} \]
  5. Final simplification85.0%

    \[\leadsto \frac{a1}{b1} \cdot \frac{a2}{b2} \]
  6. Add Preprocessing

Alternative 2: 90.9% accurate, 0.4× speedup?

\[\begin{array}{l} b2\_m = \left|b2\right| \\ b2\_s = \mathsf{copysign}\left(1, b2\right) \\ b1\_m = \left|b1\right| \\ b1\_s = \mathsf{copysign}\left(1, b1\right) \\ a2\_m = \left|a2\right| \\ a2\_s = \mathsf{copysign}\left(1, a2\right) \\ a1\_m = \left|a1\right| \\ a1\_s = \mathsf{copysign}\left(1, a1\right) \\ [a1_m, a2_m, b1_m, b2_m] = \mathsf{sort}([a1_m, a2_m, b1_m, b2_m])\\\\ [a1_m, a2_m, b1_m, b2_m] = \mathsf{sort}([a1_m, a2_m, b1_m, b2_m])\\ \\ a1\_s \cdot \left(a2\_s \cdot \left(b1\_s \cdot \left(b2\_s \cdot \begin{array}{l} \mathbf{if}\;\frac{a1\_m \cdot a2\_m}{b1\_m \cdot b2\_m} \leq 4 \cdot 10^{-97}:\\ \;\;\;\;\frac{a2\_m}{b1\_m \cdot b2\_m} \cdot a1\_m\\ \mathbf{else}:\\ \;\;\;\;\frac{a1\_m}{b1\_m \cdot b2\_m} \cdot a2\_m\\ \end{array}\right)\right)\right) \end{array} \]
b2\_m = (fabs.f64 b2)
b2\_s = (copysign.f64 #s(literal 1 binary64) b2)
b1\_m = (fabs.f64 b1)
b1\_s = (copysign.f64 #s(literal 1 binary64) b1)
a2\_m = (fabs.f64 a2)
a2\_s = (copysign.f64 #s(literal 1 binary64) a2)
a1\_m = (fabs.f64 a1)
a1\_s = (copysign.f64 #s(literal 1 binary64) a1)
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
(FPCore (a1_s a2_s b1_s b2_s a1_m a2_m b1_m b2_m)
 :precision binary64
 (*
  a1_s
  (*
   a2_s
   (*
    b1_s
    (*
     b2_s
     (if (<= (/ (* a1_m a2_m) (* b1_m b2_m)) 4e-97)
       (* (/ a2_m (* b1_m b2_m)) a1_m)
       (* (/ a1_m (* b1_m b2_m)) a2_m)))))))
b2\_m = fabs(b2);
b2\_s = copysign(1.0, b2);
b1\_m = fabs(b1);
b1\_s = copysign(1.0, b1);
a2\_m = fabs(a2);
a2\_s = copysign(1.0, a2);
a1\_m = fabs(a1);
a1\_s = copysign(1.0, a1);
assert(a1_m < a2_m && a2_m < b1_m && b1_m < b2_m);
assert(a1_m < a2_m && a2_m < b1_m && b1_m < b2_m);
double code(double a1_s, double a2_s, double b1_s, double b2_s, double a1_m, double a2_m, double b1_m, double b2_m) {
	double tmp;
	if (((a1_m * a2_m) / (b1_m * b2_m)) <= 4e-97) {
		tmp = (a2_m / (b1_m * b2_m)) * a1_m;
	} else {
		tmp = (a1_m / (b1_m * b2_m)) * a2_m;
	}
	return a1_s * (a2_s * (b1_s * (b2_s * tmp)));
}
b2\_m = abs(b2)
b2\_s = copysign(1.0d0, b2)
b1\_m = abs(b1)
b1\_s = copysign(1.0d0, b1)
a2\_m = abs(a2)
a2\_s = copysign(1.0d0, a2)
a1\_m = abs(a1)
a1\_s = copysign(1.0d0, a1)
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
real(8) function code(a1_s, a2_s, b1_s, b2_s, a1_m, a2_m, b1_m, b2_m)
    real(8), intent (in) :: a1_s
    real(8), intent (in) :: a2_s
    real(8), intent (in) :: b1_s
    real(8), intent (in) :: b2_s
    real(8), intent (in) :: a1_m
    real(8), intent (in) :: a2_m
    real(8), intent (in) :: b1_m
    real(8), intent (in) :: b2_m
    real(8) :: tmp
    if (((a1_m * a2_m) / (b1_m * b2_m)) <= 4d-97) then
        tmp = (a2_m / (b1_m * b2_m)) * a1_m
    else
        tmp = (a1_m / (b1_m * b2_m)) * a2_m
    end if
    code = a1_s * (a2_s * (b1_s * (b2_s * tmp)))
end function
b2\_m = Math.abs(b2);
b2\_s = Math.copySign(1.0, b2);
b1\_m = Math.abs(b1);
b1\_s = Math.copySign(1.0, b1);
a2\_m = Math.abs(a2);
a2\_s = Math.copySign(1.0, a2);
a1\_m = Math.abs(a1);
a1\_s = Math.copySign(1.0, a1);
assert a1_m < a2_m && a2_m < b1_m && b1_m < b2_m;
assert a1_m < a2_m && a2_m < b1_m && b1_m < b2_m;
public static double code(double a1_s, double a2_s, double b1_s, double b2_s, double a1_m, double a2_m, double b1_m, double b2_m) {
	double tmp;
	if (((a1_m * a2_m) / (b1_m * b2_m)) <= 4e-97) {
		tmp = (a2_m / (b1_m * b2_m)) * a1_m;
	} else {
		tmp = (a1_m / (b1_m * b2_m)) * a2_m;
	}
	return a1_s * (a2_s * (b1_s * (b2_s * tmp)));
}
b2\_m = math.fabs(b2)
b2\_s = math.copysign(1.0, b2)
b1\_m = math.fabs(b1)
b1\_s = math.copysign(1.0, b1)
a2\_m = math.fabs(a2)
a2\_s = math.copysign(1.0, a2)
a1\_m = math.fabs(a1)
a1\_s = math.copysign(1.0, a1)
[a1_m, a2_m, b1_m, b2_m] = sort([a1_m, a2_m, b1_m, b2_m])
[a1_m, a2_m, b1_m, b2_m] = sort([a1_m, a2_m, b1_m, b2_m])
def code(a1_s, a2_s, b1_s, b2_s, a1_m, a2_m, b1_m, b2_m):
	tmp = 0
	if ((a1_m * a2_m) / (b1_m * b2_m)) <= 4e-97:
		tmp = (a2_m / (b1_m * b2_m)) * a1_m
	else:
		tmp = (a1_m / (b1_m * b2_m)) * a2_m
	return a1_s * (a2_s * (b1_s * (b2_s * tmp)))
b2\_m = abs(b2)
b2\_s = copysign(1.0, b2)
b1\_m = abs(b1)
b1\_s = copysign(1.0, b1)
a2\_m = abs(a2)
a2\_s = copysign(1.0, a2)
a1\_m = abs(a1)
a1\_s = copysign(1.0, a1)
a1_m, a2_m, b1_m, b2_m = sort([a1_m, a2_m, b1_m, b2_m])
a1_m, a2_m, b1_m, b2_m = sort([a1_m, a2_m, b1_m, b2_m])
function code(a1_s, a2_s, b1_s, b2_s, a1_m, a2_m, b1_m, b2_m)
	tmp = 0.0
	if (Float64(Float64(a1_m * a2_m) / Float64(b1_m * b2_m)) <= 4e-97)
		tmp = Float64(Float64(a2_m / Float64(b1_m * b2_m)) * a1_m);
	else
		tmp = Float64(Float64(a1_m / Float64(b1_m * b2_m)) * a2_m);
	end
	return Float64(a1_s * Float64(a2_s * Float64(b1_s * Float64(b2_s * tmp))))
end
b2\_m = abs(b2);
b2\_s = sign(b2) * abs(1.0);
b1\_m = abs(b1);
b1\_s = sign(b1) * abs(1.0);
a2\_m = abs(a2);
a2\_s = sign(a2) * abs(1.0);
a1\_m = abs(a1);
a1\_s = sign(a1) * abs(1.0);
a1_m, a2_m, b1_m, b2_m = num2cell(sort([a1_m, a2_m, b1_m, b2_m])){:}
a1_m, a2_m, b1_m, b2_m = num2cell(sort([a1_m, a2_m, b1_m, b2_m])){:}
function tmp_2 = code(a1_s, a2_s, b1_s, b2_s, a1_m, a2_m, b1_m, b2_m)
	tmp = 0.0;
	if (((a1_m * a2_m) / (b1_m * b2_m)) <= 4e-97)
		tmp = (a2_m / (b1_m * b2_m)) * a1_m;
	else
		tmp = (a1_m / (b1_m * b2_m)) * a2_m;
	end
	tmp_2 = a1_s * (a2_s * (b1_s * (b2_s * tmp)));
end
b2\_m = N[Abs[b2], $MachinePrecision]
b2\_s = N[With[{TMP1 = Abs[1.0], TMP2 = Sign[b2]}, TMP1 * If[TMP2 == 0, 1, TMP2]], $MachinePrecision]
b1\_m = N[Abs[b1], $MachinePrecision]
b1\_s = N[With[{TMP1 = Abs[1.0], TMP2 = Sign[b1]}, TMP1 * If[TMP2 == 0, 1, TMP2]], $MachinePrecision]
a2\_m = N[Abs[a2], $MachinePrecision]
a2\_s = N[With[{TMP1 = Abs[1.0], TMP2 = Sign[a2]}, TMP1 * If[TMP2 == 0, 1, TMP2]], $MachinePrecision]
a1\_m = N[Abs[a1], $MachinePrecision]
a1\_s = N[With[{TMP1 = Abs[1.0], TMP2 = Sign[a1]}, TMP1 * If[TMP2 == 0, 1, TMP2]], $MachinePrecision]
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
code[a1$95$s_, a2$95$s_, b1$95$s_, b2$95$s_, a1$95$m_, a2$95$m_, b1$95$m_, b2$95$m_] := N[(a1$95$s * N[(a2$95$s * N[(b1$95$s * N[(b2$95$s * If[LessEqual[N[(N[(a1$95$m * a2$95$m), $MachinePrecision] / N[(b1$95$m * b2$95$m), $MachinePrecision]), $MachinePrecision], 4e-97], N[(N[(a2$95$m / N[(b1$95$m * b2$95$m), $MachinePrecision]), $MachinePrecision] * a1$95$m), $MachinePrecision], N[(N[(a1$95$m / N[(b1$95$m * b2$95$m), $MachinePrecision]), $MachinePrecision] * a2$95$m), $MachinePrecision]]), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]
\begin{array}{l}
b2\_m = \left|b2\right|
\\
b2\_s = \mathsf{copysign}\left(1, b2\right)
\\
b1\_m = \left|b1\right|
\\
b1\_s = \mathsf{copysign}\left(1, b1\right)
\\
a2\_m = \left|a2\right|
\\
a2\_s = \mathsf{copysign}\left(1, a2\right)
\\
a1\_m = \left|a1\right|
\\
a1\_s = \mathsf{copysign}\left(1, a1\right)
\\
[a1_m, a2_m, b1_m, b2_m] = \mathsf{sort}([a1_m, a2_m, b1_m, b2_m])\\\\
[a1_m, a2_m, b1_m, b2_m] = \mathsf{sort}([a1_m, a2_m, b1_m, b2_m])\\
\\
a1\_s \cdot \left(a2\_s \cdot \left(b1\_s \cdot \left(b2\_s \cdot \begin{array}{l}
\mathbf{if}\;\frac{a1\_m \cdot a2\_m}{b1\_m \cdot b2\_m} \leq 4 \cdot 10^{-97}:\\
\;\;\;\;\frac{a2\_m}{b1\_m \cdot b2\_m} \cdot a1\_m\\

\mathbf{else}:\\
\;\;\;\;\frac{a1\_m}{b1\_m \cdot b2\_m} \cdot a2\_m\\


\end{array}\right)\right)\right)
\end{array}
Derivation
  1. Split input into 2 regimes
  2. if (/.f64 (*.f64 a1 a2) (*.f64 b1 b2)) < 4.00000000000000014e-97

    1. Initial program 86.8%

      \[\frac{a1 \cdot a2}{b1 \cdot b2} \]
    2. Add Preprocessing
    3. Step-by-step derivation
      1. lift-/.f64N/A

        \[\leadsto \color{blue}{\frac{a1 \cdot a2}{b1 \cdot b2}} \]
      2. lift-*.f64N/A

        \[\leadsto \frac{\color{blue}{a1 \cdot a2}}{b1 \cdot b2} \]
      3. associate-/l*N/A

        \[\leadsto \color{blue}{a1 \cdot \frac{a2}{b1 \cdot b2}} \]
      4. *-commutativeN/A

        \[\leadsto \color{blue}{\frac{a2}{b1 \cdot b2} \cdot a1} \]
      5. lower-*.f64N/A

        \[\leadsto \color{blue}{\frac{a2}{b1 \cdot b2} \cdot a1} \]
      6. lift-*.f64N/A

        \[\leadsto \frac{a2}{\color{blue}{b1 \cdot b2}} \cdot a1 \]
      7. associate-/l/N/A

        \[\leadsto \color{blue}{\frac{\frac{a2}{b2}}{b1}} \cdot a1 \]
      8. lower-/.f64N/A

        \[\leadsto \color{blue}{\frac{\frac{a2}{b2}}{b1}} \cdot a1 \]
      9. lower-/.f6487.9

        \[\leadsto \frac{\color{blue}{\frac{a2}{b2}}}{b1} \cdot a1 \]
    4. Applied rewrites87.9%

      \[\leadsto \color{blue}{\frac{\frac{a2}{b2}}{b1} \cdot a1} \]
    5. Step-by-step derivation
      1. lift-/.f64N/A

        \[\leadsto \color{blue}{\frac{\frac{a2}{b2}}{b1}} \cdot a1 \]
      2. lift-/.f64N/A

        \[\leadsto \frac{\color{blue}{\frac{a2}{b2}}}{b1} \cdot a1 \]
      3. associate-/r*N/A

        \[\leadsto \color{blue}{\frac{a2}{b2 \cdot b1}} \cdot a1 \]
      4. lower-/.f64N/A

        \[\leadsto \color{blue}{\frac{a2}{b2 \cdot b1}} \cdot a1 \]
      5. *-commutativeN/A

        \[\leadsto \frac{a2}{\color{blue}{b1 \cdot b2}} \cdot a1 \]
      6. lower-*.f6488.8

        \[\leadsto \frac{a2}{\color{blue}{b1 \cdot b2}} \cdot a1 \]
    6. Applied rewrites88.8%

      \[\leadsto \color{blue}{\frac{a2}{b1 \cdot b2}} \cdot a1 \]

    if 4.00000000000000014e-97 < (/.f64 (*.f64 a1 a2) (*.f64 b1 b2))

    1. Initial program 86.9%

      \[\frac{a1 \cdot a2}{b1 \cdot b2} \]
    2. Add Preprocessing
    3. Step-by-step derivation
      1. lift-/.f64N/A

        \[\leadsto \color{blue}{\frac{a1 \cdot a2}{b1 \cdot b2}} \]
      2. lift-*.f64N/A

        \[\leadsto \frac{\color{blue}{a1 \cdot a2}}{b1 \cdot b2} \]
      3. associate-/l*N/A

        \[\leadsto \color{blue}{a1 \cdot \frac{a2}{b1 \cdot b2}} \]
      4. *-commutativeN/A

        \[\leadsto \color{blue}{\frac{a2}{b1 \cdot b2} \cdot a1} \]
      5. lower-*.f64N/A

        \[\leadsto \color{blue}{\frac{a2}{b1 \cdot b2} \cdot a1} \]
      6. lift-*.f64N/A

        \[\leadsto \frac{a2}{\color{blue}{b1 \cdot b2}} \cdot a1 \]
      7. associate-/l/N/A

        \[\leadsto \color{blue}{\frac{\frac{a2}{b2}}{b1}} \cdot a1 \]
      8. lower-/.f64N/A

        \[\leadsto \color{blue}{\frac{\frac{a2}{b2}}{b1}} \cdot a1 \]
      9. lower-/.f6489.0

        \[\leadsto \frac{\color{blue}{\frac{a2}{b2}}}{b1} \cdot a1 \]
    4. Applied rewrites89.0%

      \[\leadsto \color{blue}{\frac{\frac{a2}{b2}}{b1} \cdot a1} \]
    5. Step-by-step derivation
      1. lift-/.f64N/A

        \[\leadsto \color{blue}{\frac{\frac{a2}{b2}}{b1}} \cdot a1 \]
      2. lift-/.f64N/A

        \[\leadsto \frac{\color{blue}{\frac{a2}{b2}}}{b1} \cdot a1 \]
      3. associate-/r*N/A

        \[\leadsto \color{blue}{\frac{a2}{b2 \cdot b1}} \cdot a1 \]
      4. lower-/.f64N/A

        \[\leadsto \color{blue}{\frac{a2}{b2 \cdot b1}} \cdot a1 \]
      5. *-commutativeN/A

        \[\leadsto \frac{a2}{\color{blue}{b1 \cdot b2}} \cdot a1 \]
      6. lower-*.f6485.2

        \[\leadsto \frac{a2}{\color{blue}{b1 \cdot b2}} \cdot a1 \]
    6. Applied rewrites85.2%

      \[\leadsto \color{blue}{\frac{a2}{b1 \cdot b2}} \cdot a1 \]
    7. Taylor expanded in a1 around 0

      \[\leadsto \color{blue}{\frac{a1 \cdot a2}{b1 \cdot b2}} \]
    8. Step-by-step derivation
      1. *-commutativeN/A

        \[\leadsto \frac{\color{blue}{a2 \cdot a1}}{b1 \cdot b2} \]
      2. associate-/l*N/A

        \[\leadsto \color{blue}{a2 \cdot \frac{a1}{b1 \cdot b2}} \]
      3. lower-*.f64N/A

        \[\leadsto \color{blue}{a2 \cdot \frac{a1}{b1 \cdot b2}} \]
      4. lower-/.f64N/A

        \[\leadsto a2 \cdot \color{blue}{\frac{a1}{b1 \cdot b2}} \]
      5. *-commutativeN/A

        \[\leadsto a2 \cdot \frac{a1}{\color{blue}{b2 \cdot b1}} \]
      6. lower-*.f6480.6

        \[\leadsto a2 \cdot \frac{a1}{\color{blue}{b2 \cdot b1}} \]
    9. Applied rewrites80.6%

      \[\leadsto \color{blue}{a2 \cdot \frac{a1}{b2 \cdot b1}} \]
  3. Recombined 2 regimes into one program.
  4. Final simplification86.5%

    \[\leadsto \begin{array}{l} \mathbf{if}\;\frac{a1 \cdot a2}{b1 \cdot b2} \leq 4 \cdot 10^{-97}:\\ \;\;\;\;\frac{a2}{b1 \cdot b2} \cdot a1\\ \mathbf{else}:\\ \;\;\;\;\frac{a1}{b1 \cdot b2} \cdot a2\\ \end{array} \]
  5. Add Preprocessing

Alternative 3: 86.5% accurate, 1.0× speedup?

\[\begin{array}{l} b2\_m = \left|b2\right| \\ b2\_s = \mathsf{copysign}\left(1, b2\right) \\ b1\_m = \left|b1\right| \\ b1\_s = \mathsf{copysign}\left(1, b1\right) \\ a2\_m = \left|a2\right| \\ a2\_s = \mathsf{copysign}\left(1, a2\right) \\ a1\_m = \left|a1\right| \\ a1\_s = \mathsf{copysign}\left(1, a1\right) \\ [a1_m, a2_m, b1_m, b2_m] = \mathsf{sort}([a1_m, a2_m, b1_m, b2_m])\\\\ [a1_m, a2_m, b1_m, b2_m] = \mathsf{sort}([a1_m, a2_m, b1_m, b2_m])\\ \\ a1\_s \cdot \left(a2\_s \cdot \left(b1\_s \cdot \left(b2\_s \cdot \left(\frac{a1\_m}{b1\_m \cdot b2\_m} \cdot a2\_m\right)\right)\right)\right) \end{array} \]
b2\_m = (fabs.f64 b2)
b2\_s = (copysign.f64 #s(literal 1 binary64) b2)
b1\_m = (fabs.f64 b1)
b1\_s = (copysign.f64 #s(literal 1 binary64) b1)
a2\_m = (fabs.f64 a2)
a2\_s = (copysign.f64 #s(literal 1 binary64) a2)
a1\_m = (fabs.f64 a1)
a1\_s = (copysign.f64 #s(literal 1 binary64) a1)
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
(FPCore (a1_s a2_s b1_s b2_s a1_m a2_m b1_m b2_m)
 :precision binary64
 (* a1_s (* a2_s (* b1_s (* b2_s (* (/ a1_m (* b1_m b2_m)) a2_m))))))
b2\_m = fabs(b2);
b2\_s = copysign(1.0, b2);
b1\_m = fabs(b1);
b1\_s = copysign(1.0, b1);
a2\_m = fabs(a2);
a2\_s = copysign(1.0, a2);
a1\_m = fabs(a1);
a1\_s = copysign(1.0, a1);
assert(a1_m < a2_m && a2_m < b1_m && b1_m < b2_m);
assert(a1_m < a2_m && a2_m < b1_m && b1_m < b2_m);
double code(double a1_s, double a2_s, double b1_s, double b2_s, double a1_m, double a2_m, double b1_m, double b2_m) {
	return a1_s * (a2_s * (b1_s * (b2_s * ((a1_m / (b1_m * b2_m)) * a2_m))));
}
b2\_m = abs(b2)
b2\_s = copysign(1.0d0, b2)
b1\_m = abs(b1)
b1\_s = copysign(1.0d0, b1)
a2\_m = abs(a2)
a2\_s = copysign(1.0d0, a2)
a1\_m = abs(a1)
a1\_s = copysign(1.0d0, a1)
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
real(8) function code(a1_s, a2_s, b1_s, b2_s, a1_m, a2_m, b1_m, b2_m)
    real(8), intent (in) :: a1_s
    real(8), intent (in) :: a2_s
    real(8), intent (in) :: b1_s
    real(8), intent (in) :: b2_s
    real(8), intent (in) :: a1_m
    real(8), intent (in) :: a2_m
    real(8), intent (in) :: b1_m
    real(8), intent (in) :: b2_m
    code = a1_s * (a2_s * (b1_s * (b2_s * ((a1_m / (b1_m * b2_m)) * a2_m))))
end function
b2\_m = Math.abs(b2);
b2\_s = Math.copySign(1.0, b2);
b1\_m = Math.abs(b1);
b1\_s = Math.copySign(1.0, b1);
a2\_m = Math.abs(a2);
a2\_s = Math.copySign(1.0, a2);
a1\_m = Math.abs(a1);
a1\_s = Math.copySign(1.0, a1);
assert a1_m < a2_m && a2_m < b1_m && b1_m < b2_m;
assert a1_m < a2_m && a2_m < b1_m && b1_m < b2_m;
public static double code(double a1_s, double a2_s, double b1_s, double b2_s, double a1_m, double a2_m, double b1_m, double b2_m) {
	return a1_s * (a2_s * (b1_s * (b2_s * ((a1_m / (b1_m * b2_m)) * a2_m))));
}
b2\_m = math.fabs(b2)
b2\_s = math.copysign(1.0, b2)
b1\_m = math.fabs(b1)
b1\_s = math.copysign(1.0, b1)
a2\_m = math.fabs(a2)
a2\_s = math.copysign(1.0, a2)
a1\_m = math.fabs(a1)
a1\_s = math.copysign(1.0, a1)
[a1_m, a2_m, b1_m, b2_m] = sort([a1_m, a2_m, b1_m, b2_m])
[a1_m, a2_m, b1_m, b2_m] = sort([a1_m, a2_m, b1_m, b2_m])
def code(a1_s, a2_s, b1_s, b2_s, a1_m, a2_m, b1_m, b2_m):
	return a1_s * (a2_s * (b1_s * (b2_s * ((a1_m / (b1_m * b2_m)) * a2_m))))
b2\_m = abs(b2)
b2\_s = copysign(1.0, b2)
b1\_m = abs(b1)
b1\_s = copysign(1.0, b1)
a2\_m = abs(a2)
a2\_s = copysign(1.0, a2)
a1\_m = abs(a1)
a1\_s = copysign(1.0, a1)
a1_m, a2_m, b1_m, b2_m = sort([a1_m, a2_m, b1_m, b2_m])
a1_m, a2_m, b1_m, b2_m = sort([a1_m, a2_m, b1_m, b2_m])
function code(a1_s, a2_s, b1_s, b2_s, a1_m, a2_m, b1_m, b2_m)
	return Float64(a1_s * Float64(a2_s * Float64(b1_s * Float64(b2_s * Float64(Float64(a1_m / Float64(b1_m * b2_m)) * a2_m)))))
end
b2\_m = abs(b2);
b2\_s = sign(b2) * abs(1.0);
b1\_m = abs(b1);
b1\_s = sign(b1) * abs(1.0);
a2\_m = abs(a2);
a2\_s = sign(a2) * abs(1.0);
a1\_m = abs(a1);
a1\_s = sign(a1) * abs(1.0);
a1_m, a2_m, b1_m, b2_m = num2cell(sort([a1_m, a2_m, b1_m, b2_m])){:}
a1_m, a2_m, b1_m, b2_m = num2cell(sort([a1_m, a2_m, b1_m, b2_m])){:}
function tmp = code(a1_s, a2_s, b1_s, b2_s, a1_m, a2_m, b1_m, b2_m)
	tmp = a1_s * (a2_s * (b1_s * (b2_s * ((a1_m / (b1_m * b2_m)) * a2_m))));
end
b2\_m = N[Abs[b2], $MachinePrecision]
b2\_s = N[With[{TMP1 = Abs[1.0], TMP2 = Sign[b2]}, TMP1 * If[TMP2 == 0, 1, TMP2]], $MachinePrecision]
b1\_m = N[Abs[b1], $MachinePrecision]
b1\_s = N[With[{TMP1 = Abs[1.0], TMP2 = Sign[b1]}, TMP1 * If[TMP2 == 0, 1, TMP2]], $MachinePrecision]
a2\_m = N[Abs[a2], $MachinePrecision]
a2\_s = N[With[{TMP1 = Abs[1.0], TMP2 = Sign[a2]}, TMP1 * If[TMP2 == 0, 1, TMP2]], $MachinePrecision]
a1\_m = N[Abs[a1], $MachinePrecision]
a1\_s = N[With[{TMP1 = Abs[1.0], TMP2 = Sign[a1]}, TMP1 * If[TMP2 == 0, 1, TMP2]], $MachinePrecision]
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
NOTE: a1_m, a2_m, b1_m, and b2_m should be sorted in increasing order before calling this function.
code[a1$95$s_, a2$95$s_, b1$95$s_, b2$95$s_, a1$95$m_, a2$95$m_, b1$95$m_, b2$95$m_] := N[(a1$95$s * N[(a2$95$s * N[(b1$95$s * N[(b2$95$s * N[(N[(a1$95$m / N[(b1$95$m * b2$95$m), $MachinePrecision]), $MachinePrecision] * a2$95$m), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]
\begin{array}{l}
b2\_m = \left|b2\right|
\\
b2\_s = \mathsf{copysign}\left(1, b2\right)
\\
b1\_m = \left|b1\right|
\\
b1\_s = \mathsf{copysign}\left(1, b1\right)
\\
a2\_m = \left|a2\right|
\\
a2\_s = \mathsf{copysign}\left(1, a2\right)
\\
a1\_m = \left|a1\right|
\\
a1\_s = \mathsf{copysign}\left(1, a1\right)
\\
[a1_m, a2_m, b1_m, b2_m] = \mathsf{sort}([a1_m, a2_m, b1_m, b2_m])\\\\
[a1_m, a2_m, b1_m, b2_m] = \mathsf{sort}([a1_m, a2_m, b1_m, b2_m])\\
\\
a1\_s \cdot \left(a2\_s \cdot \left(b1\_s \cdot \left(b2\_s \cdot \left(\frac{a1\_m}{b1\_m \cdot b2\_m} \cdot a2\_m\right)\right)\right)\right)
\end{array}
Derivation
  1. Initial program 86.8%

    \[\frac{a1 \cdot a2}{b1 \cdot b2} \]
  2. Add Preprocessing
  3. Step-by-step derivation
    1. lift-/.f64N/A

      \[\leadsto \color{blue}{\frac{a1 \cdot a2}{b1 \cdot b2}} \]
    2. lift-*.f64N/A

      \[\leadsto \frac{\color{blue}{a1 \cdot a2}}{b1 \cdot b2} \]
    3. associate-/l*N/A

      \[\leadsto \color{blue}{a1 \cdot \frac{a2}{b1 \cdot b2}} \]
    4. *-commutativeN/A

      \[\leadsto \color{blue}{\frac{a2}{b1 \cdot b2} \cdot a1} \]
    5. lower-*.f64N/A

      \[\leadsto \color{blue}{\frac{a2}{b1 \cdot b2} \cdot a1} \]
    6. lift-*.f64N/A

      \[\leadsto \frac{a2}{\color{blue}{b1 \cdot b2}} \cdot a1 \]
    7. associate-/l/N/A

      \[\leadsto \color{blue}{\frac{\frac{a2}{b2}}{b1}} \cdot a1 \]
    8. lower-/.f64N/A

      \[\leadsto \color{blue}{\frac{\frac{a2}{b2}}{b1}} \cdot a1 \]
    9. lower-/.f6488.2

      \[\leadsto \frac{\color{blue}{\frac{a2}{b2}}}{b1} \cdot a1 \]
  4. Applied rewrites88.2%

    \[\leadsto \color{blue}{\frac{\frac{a2}{b2}}{b1} \cdot a1} \]
  5. Step-by-step derivation
    1. lift-/.f64N/A

      \[\leadsto \color{blue}{\frac{\frac{a2}{b2}}{b1}} \cdot a1 \]
    2. lift-/.f64N/A

      \[\leadsto \frac{\color{blue}{\frac{a2}{b2}}}{b1} \cdot a1 \]
    3. associate-/r*N/A

      \[\leadsto \color{blue}{\frac{a2}{b2 \cdot b1}} \cdot a1 \]
    4. lower-/.f64N/A

      \[\leadsto \color{blue}{\frac{a2}{b2 \cdot b1}} \cdot a1 \]
    5. *-commutativeN/A

      \[\leadsto \frac{a2}{\color{blue}{b1 \cdot b2}} \cdot a1 \]
    6. lower-*.f6487.8

      \[\leadsto \frac{a2}{\color{blue}{b1 \cdot b2}} \cdot a1 \]
  6. Applied rewrites87.8%

    \[\leadsto \color{blue}{\frac{a2}{b1 \cdot b2}} \cdot a1 \]
  7. Taylor expanded in a1 around 0

    \[\leadsto \color{blue}{\frac{a1 \cdot a2}{b1 \cdot b2}} \]
  8. Step-by-step derivation
    1. *-commutativeN/A

      \[\leadsto \frac{\color{blue}{a2 \cdot a1}}{b1 \cdot b2} \]
    2. associate-/l*N/A

      \[\leadsto \color{blue}{a2 \cdot \frac{a1}{b1 \cdot b2}} \]
    3. lower-*.f64N/A

      \[\leadsto \color{blue}{a2 \cdot \frac{a1}{b1 \cdot b2}} \]
    4. lower-/.f64N/A

      \[\leadsto a2 \cdot \color{blue}{\frac{a1}{b1 \cdot b2}} \]
    5. *-commutativeN/A

      \[\leadsto a2 \cdot \frac{a1}{\color{blue}{b2 \cdot b1}} \]
    6. lower-*.f6484.0

      \[\leadsto a2 \cdot \frac{a1}{\color{blue}{b2 \cdot b1}} \]
  9. Applied rewrites84.0%

    \[\leadsto \color{blue}{a2 \cdot \frac{a1}{b2 \cdot b1}} \]
  10. Final simplification84.0%

    \[\leadsto \frac{a1}{b1 \cdot b2} \cdot a2 \]
  11. Add Preprocessing

Developer Target 1: 97.9% accurate, 0.8× speedup?

\[\begin{array}{l} \\ \frac{a1}{b1} \cdot \frac{a2}{b2} \end{array} \]
(FPCore (a1 a2 b1 b2) :precision binary64 (* (/ a1 b1) (/ a2 b2)))
double code(double a1, double a2, double b1, double b2) {
	return (a1 / b1) * (a2 / b2);
}
real(8) function code(a1, a2, b1, b2)
    real(8), intent (in) :: a1
    real(8), intent (in) :: a2
    real(8), intent (in) :: b1
    real(8), intent (in) :: b2
    code = (a1 / b1) * (a2 / b2)
end function
public static double code(double a1, double a2, double b1, double b2) {
	return (a1 / b1) * (a2 / b2);
}
def code(a1, a2, b1, b2):
	return (a1 / b1) * (a2 / b2)
function code(a1, a2, b1, b2)
	return Float64(Float64(a1 / b1) * Float64(a2 / b2))
end
function tmp = code(a1, a2, b1, b2)
	tmp = (a1 / b1) * (a2 / b2);
end
code[a1_, a2_, b1_, b2_] := N[(N[(a1 / b1), $MachinePrecision] * N[(a2 / b2), $MachinePrecision]), $MachinePrecision]
\begin{array}{l}

\\
\frac{a1}{b1} \cdot \frac{a2}{b2}
\end{array}

Reproduce

?
herbie shell --seed 2024284 
(FPCore (a1 a2 b1 b2)
  :name "Quotient of products"
  :precision binary64

  :alt
  (! :herbie-platform default (* (/ a1 b1) (/ a2 b2)))

  (/ (* a1 a2) (* b1 b2)))