
(FPCore (x y z) :precision binary64 (- (+ (- x (* (+ y 0.5) (log y))) y) z))
double code(double x, double y, double z) {
return ((x - ((y + 0.5) * log(y))) + y) - z;
}
real(8) function code(x, y, z)
real(8), intent (in) :: x
real(8), intent (in) :: y
real(8), intent (in) :: z
code = ((x - ((y + 0.5d0) * log(y))) + y) - z
end function
public static double code(double x, double y, double z) {
return ((x - ((y + 0.5) * Math.log(y))) + y) - z;
}
def code(x, y, z): return ((x - ((y + 0.5) * math.log(y))) + y) - z
function code(x, y, z) return Float64(Float64(Float64(x - Float64(Float64(y + 0.5) * log(y))) + y) - z) end
function tmp = code(x, y, z) tmp = ((x - ((y + 0.5) * log(y))) + y) - z; end
code[x_, y_, z_] := N[(N[(N[(x - N[(N[(y + 0.5), $MachinePrecision] * N[Log[y], $MachinePrecision]), $MachinePrecision]), $MachinePrecision] + y), $MachinePrecision] - z), $MachinePrecision]
\begin{array}{l}
\\
\left(\left(x - \left(y + 0.5\right) \cdot \log y\right) + y\right) - z
\end{array}
Sampling outcomes in binary64 precision:
Herbie found 9 alternatives:
| Alternative | Accuracy | Speedup |
|---|
(FPCore (x y z) :precision binary64 (- (+ (- x (* (+ y 0.5) (log y))) y) z))
double code(double x, double y, double z) {
return ((x - ((y + 0.5) * log(y))) + y) - z;
}
real(8) function code(x, y, z)
real(8), intent (in) :: x
real(8), intent (in) :: y
real(8), intent (in) :: z
code = ((x - ((y + 0.5d0) * log(y))) + y) - z
end function
public static double code(double x, double y, double z) {
return ((x - ((y + 0.5) * Math.log(y))) + y) - z;
}
def code(x, y, z): return ((x - ((y + 0.5) * math.log(y))) + y) - z
function code(x, y, z) return Float64(Float64(Float64(x - Float64(Float64(y + 0.5) * log(y))) + y) - z) end
function tmp = code(x, y, z) tmp = ((x - ((y + 0.5) * log(y))) + y) - z; end
code[x_, y_, z_] := N[(N[(N[(x - N[(N[(y + 0.5), $MachinePrecision] * N[Log[y], $MachinePrecision]), $MachinePrecision]), $MachinePrecision] + y), $MachinePrecision] - z), $MachinePrecision]
\begin{array}{l}
\\
\left(\left(x - \left(y + 0.5\right) \cdot \log y\right) + y\right) - z
\end{array}
(FPCore (x y z) :precision binary64 (- (+ (- x (* (log y) (+ 0.5 y))) y) z))
double code(double x, double y, double z) {
return ((x - (log(y) * (0.5 + y))) + y) - z;
}
real(8) function code(x, y, z)
real(8), intent (in) :: x
real(8), intent (in) :: y
real(8), intent (in) :: z
code = ((x - (log(y) * (0.5d0 + y))) + y) - z
end function
public static double code(double x, double y, double z) {
return ((x - (Math.log(y) * (0.5 + y))) + y) - z;
}
def code(x, y, z): return ((x - (math.log(y) * (0.5 + y))) + y) - z
function code(x, y, z) return Float64(Float64(Float64(x - Float64(log(y) * Float64(0.5 + y))) + y) - z) end
function tmp = code(x, y, z) tmp = ((x - (log(y) * (0.5 + y))) + y) - z; end
code[x_, y_, z_] := N[(N[(N[(x - N[(N[Log[y], $MachinePrecision] * N[(0.5 + y), $MachinePrecision]), $MachinePrecision]), $MachinePrecision] + y), $MachinePrecision] - z), $MachinePrecision]
\begin{array}{l}
\\
\left(\left(x - \log y \cdot \left(0.5 + y\right)\right) + y\right) - z
\end{array}
Initial program 99.9%
Final simplification99.9%
(FPCore (x y z)
:precision binary64
(let* ((t_0 (+ (- x (* (log y) (+ 0.5 y))) y)))
(if (<= t_0 -1e+65)
(* (- 1.0 (log y)) y)
(if (<= t_0 350.0) (fma -0.5 (log y) (- z)) (- (+ (* 1.0 x) y) z)))))
double code(double x, double y, double z) {
double t_0 = (x - (log(y) * (0.5 + y))) + y;
double tmp;
if (t_0 <= -1e+65) {
tmp = (1.0 - log(y)) * y;
} else if (t_0 <= 350.0) {
tmp = fma(-0.5, log(y), -z);
} else {
tmp = ((1.0 * x) + y) - z;
}
return tmp;
}
function code(x, y, z) t_0 = Float64(Float64(x - Float64(log(y) * Float64(0.5 + y))) + y) tmp = 0.0 if (t_0 <= -1e+65) tmp = Float64(Float64(1.0 - log(y)) * y); elseif (t_0 <= 350.0) tmp = fma(-0.5, log(y), Float64(-z)); else tmp = Float64(Float64(Float64(1.0 * x) + y) - z); end return tmp end
code[x_, y_, z_] := Block[{t$95$0 = N[(N[(x - N[(N[Log[y], $MachinePrecision] * N[(0.5 + y), $MachinePrecision]), $MachinePrecision]), $MachinePrecision] + y), $MachinePrecision]}, If[LessEqual[t$95$0, -1e+65], N[(N[(1.0 - N[Log[y], $MachinePrecision]), $MachinePrecision] * y), $MachinePrecision], If[LessEqual[t$95$0, 350.0], N[(-0.5 * N[Log[y], $MachinePrecision] + (-z)), $MachinePrecision], N[(N[(N[(1.0 * x), $MachinePrecision] + y), $MachinePrecision] - z), $MachinePrecision]]]]
\begin{array}{l}
\\
\begin{array}{l}
t_0 := \left(x - \log y \cdot \left(0.5 + y\right)\right) + y\\
\mathbf{if}\;t\_0 \leq -1 \cdot 10^{+65}:\\
\;\;\;\;\left(1 - \log y\right) \cdot y\\
\mathbf{elif}\;t\_0 \leq 350:\\
\;\;\;\;\mathsf{fma}\left(-0.5, \log y, -z\right)\\
\mathbf{else}:\\
\;\;\;\;\left(1 \cdot x + y\right) - z\\
\end{array}
\end{array}
if (+.f64 (-.f64 x (*.f64 (+.f64 y #s(literal 1/2 binary64)) (log.f64 y))) y) < -9.9999999999999999e64Initial program 99.8%
Taylor expanded in y around inf
*-commutativeN/A
mul-1-negN/A
log-recN/A
remove-double-negN/A
lower-*.f64N/A
lower--.f64N/A
lower-log.f6458.6
Applied rewrites58.6%
if -9.9999999999999999e64 < (+.f64 (-.f64 x (*.f64 (+.f64 y #s(literal 1/2 binary64)) (log.f64 y))) y) < 350Initial program 99.9%
Taylor expanded in x around 0
lower--.f64N/A
+-commutativeN/A
*-commutativeN/A
lower-fma.f64N/A
lower-+.f64N/A
lower-log.f6495.1
Applied rewrites95.1%
Taylor expanded in y around 0
Applied rewrites90.4%
if 350 < (+.f64 (-.f64 x (*.f64 (+.f64 y #s(literal 1/2 binary64)) (log.f64 y))) y) Initial program 100.0%
lift-*.f64N/A
*-commutativeN/A
lift-+.f64N/A
flip3-+N/A
clear-numN/A
un-div-invN/A
lower-/.f64N/A
clear-numN/A
flip3-+N/A
lift-+.f64N/A
lower-/.f64100.0
lift-+.f64N/A
+-commutativeN/A
lower-+.f64100.0
Applied rewrites100.0%
Taylor expanded in y around inf
mul-1-negN/A
*-commutativeN/A
distribute-lft-neg-inN/A
log-recN/A
remove-double-negN/A
lower-*.f64N/A
lower-log.f6499.1
Applied rewrites99.1%
Taylor expanded in x around inf
*-commutativeN/A
lower-*.f64N/A
+-commutativeN/A
mul-1-negN/A
associate-/l*N/A
*-commutativeN/A
distribute-lft-neg-inN/A
lower-fma.f64N/A
distribute-neg-fracN/A
lower-/.f64N/A
distribute-neg-inN/A
metadata-evalN/A
unsub-negN/A
lower--.f64N/A
lower-log.f64100.0
Applied rewrites100.0%
Taylor expanded in x around inf
Applied rewrites96.2%
Final simplification76.0%
(FPCore (x y z)
:precision binary64
(let* ((t_0 (- (+ (* 1.0 x) y) z)))
(if (<= x -54.0)
t_0
(if (<= x 3200000000.0) (fma -0.5 (log y) (- z)) t_0))))
double code(double x, double y, double z) {
double t_0 = ((1.0 * x) + y) - z;
double tmp;
if (x <= -54.0) {
tmp = t_0;
} else if (x <= 3200000000.0) {
tmp = fma(-0.5, log(y), -z);
} else {
tmp = t_0;
}
return tmp;
}
function code(x, y, z) t_0 = Float64(Float64(Float64(1.0 * x) + y) - z) tmp = 0.0 if (x <= -54.0) tmp = t_0; elseif (x <= 3200000000.0) tmp = fma(-0.5, log(y), Float64(-z)); else tmp = t_0; end return tmp end
code[x_, y_, z_] := Block[{t$95$0 = N[(N[(N[(1.0 * x), $MachinePrecision] + y), $MachinePrecision] - z), $MachinePrecision]}, If[LessEqual[x, -54.0], t$95$0, If[LessEqual[x, 3200000000.0], N[(-0.5 * N[Log[y], $MachinePrecision] + (-z)), $MachinePrecision], t$95$0]]]
\begin{array}{l}
\\
\begin{array}{l}
t_0 := \left(1 \cdot x + y\right) - z\\
\mathbf{if}\;x \leq -54:\\
\;\;\;\;t\_0\\
\mathbf{elif}\;x \leq 3200000000:\\
\;\;\;\;\mathsf{fma}\left(-0.5, \log y, -z\right)\\
\mathbf{else}:\\
\;\;\;\;t\_0\\
\end{array}
\end{array}
if x < -54 or 3.2e9 < x Initial program 99.9%
lift-*.f64N/A
*-commutativeN/A
lift-+.f64N/A
flip3-+N/A
clear-numN/A
un-div-invN/A
lower-/.f64N/A
clear-numN/A
flip3-+N/A
lift-+.f64N/A
lower-/.f6499.9
lift-+.f64N/A
+-commutativeN/A
lower-+.f6499.9
Applied rewrites99.9%
Taylor expanded in y around inf
mul-1-negN/A
*-commutativeN/A
distribute-lft-neg-inN/A
log-recN/A
remove-double-negN/A
lower-*.f64N/A
lower-log.f6498.2
Applied rewrites98.2%
Taylor expanded in x around inf
*-commutativeN/A
lower-*.f64N/A
+-commutativeN/A
mul-1-negN/A
associate-/l*N/A
*-commutativeN/A
distribute-lft-neg-inN/A
lower-fma.f64N/A
distribute-neg-fracN/A
lower-/.f64N/A
distribute-neg-inN/A
metadata-evalN/A
unsub-negN/A
lower--.f64N/A
lower-log.f6499.9
Applied rewrites99.9%
Taylor expanded in x around inf
Applied rewrites77.3%
if -54 < x < 3.2e9Initial program 99.8%
Taylor expanded in x around 0
lower--.f64N/A
+-commutativeN/A
*-commutativeN/A
lower-fma.f64N/A
lower-+.f64N/A
lower-log.f6499.6
Applied rewrites99.6%
Taylor expanded in y around 0
Applied rewrites62.4%
(FPCore (x y z) :precision binary64 (if (<= y 8.2e-18) (- (fma -0.5 (log y) x) z) (- (+ (- x (* (log y) y)) y) z)))
double code(double x, double y, double z) {
double tmp;
if (y <= 8.2e-18) {
tmp = fma(-0.5, log(y), x) - z;
} else {
tmp = ((x - (log(y) * y)) + y) - z;
}
return tmp;
}
function code(x, y, z) tmp = 0.0 if (y <= 8.2e-18) tmp = Float64(fma(-0.5, log(y), x) - z); else tmp = Float64(Float64(Float64(x - Float64(log(y) * y)) + y) - z); end return tmp end
code[x_, y_, z_] := If[LessEqual[y, 8.2e-18], N[(N[(-0.5 * N[Log[y], $MachinePrecision] + x), $MachinePrecision] - z), $MachinePrecision], N[(N[(N[(x - N[(N[Log[y], $MachinePrecision] * y), $MachinePrecision]), $MachinePrecision] + y), $MachinePrecision] - z), $MachinePrecision]]
\begin{array}{l}
\\
\begin{array}{l}
\mathbf{if}\;y \leq 8.2 \cdot 10^{-18}:\\
\;\;\;\;\mathsf{fma}\left(-0.5, \log y, x\right) - z\\
\mathbf{else}:\\
\;\;\;\;\left(\left(x - \log y \cdot y\right) + y\right) - z\\
\end{array}
\end{array}
if y < 8.1999999999999995e-18Initial program 100.0%
Taylor expanded in y around 0
+-commutativeN/A
associate--r+N/A
lower--.f64N/A
sub-negN/A
+-commutativeN/A
distribute-lft-neg-inN/A
metadata-evalN/A
lower-fma.f64N/A
lower-log.f64100.0
Applied rewrites100.0%
if 8.1999999999999995e-18 < y Initial program 99.8%
Taylor expanded in y around inf
*-commutativeN/A
associate-*r*N/A
mul-1-negN/A
log-recN/A
remove-double-negN/A
lower-*.f64N/A
lower-log.f6499.8
Applied rewrites99.8%
(FPCore (x y z) :precision binary64 (if (<= y 9.5e+61) (- (fma -0.5 (log y) x) z) (fma (- -0.5 y) (log y) (+ y x))))
double code(double x, double y, double z) {
double tmp;
if (y <= 9.5e+61) {
tmp = fma(-0.5, log(y), x) - z;
} else {
tmp = fma((-0.5 - y), log(y), (y + x));
}
return tmp;
}
function code(x, y, z) tmp = 0.0 if (y <= 9.5e+61) tmp = Float64(fma(-0.5, log(y), x) - z); else tmp = fma(Float64(-0.5 - y), log(y), Float64(y + x)); end return tmp end
code[x_, y_, z_] := If[LessEqual[y, 9.5e+61], N[(N[(-0.5 * N[Log[y], $MachinePrecision] + x), $MachinePrecision] - z), $MachinePrecision], N[(N[(-0.5 - y), $MachinePrecision] * N[Log[y], $MachinePrecision] + N[(y + x), $MachinePrecision]), $MachinePrecision]]
\begin{array}{l}
\\
\begin{array}{l}
\mathbf{if}\;y \leq 9.5 \cdot 10^{+61}:\\
\;\;\;\;\mathsf{fma}\left(-0.5, \log y, x\right) - z\\
\mathbf{else}:\\
\;\;\;\;\mathsf{fma}\left(-0.5 - y, \log y, y + x\right)\\
\end{array}
\end{array}
if y < 9.49999999999999959e61Initial program 99.9%
Taylor expanded in y around 0
+-commutativeN/A
associate--r+N/A
lower--.f64N/A
sub-negN/A
+-commutativeN/A
distribute-lft-neg-inN/A
metadata-evalN/A
lower-fma.f64N/A
lower-log.f6497.2
Applied rewrites97.2%
if 9.49999999999999959e61 < y Initial program 99.8%
lift--.f64N/A
flip--N/A
clear-numN/A
lower-/.f64N/A
clear-numN/A
flip--N/A
lift--.f64N/A
lower-/.f6499.7
lift--.f64N/A
sub-negN/A
+-commutativeN/A
lift-*.f64N/A
distribute-lft-neg-inN/A
lower-fma.f64N/A
Applied rewrites99.7%
Taylor expanded in y around inf
log-recN/A
sub-negN/A
*-commutativeN/A
lower-*.f64N/A
lower--.f64N/A
lower-log.f6464.9
Applied rewrites64.9%
Taylor expanded in z around 0
mul-1-negN/A
sub-negN/A
associate--l+N/A
sub-negN/A
+-commutativeN/A
*-commutativeN/A
distribute-lft-neg-inN/A
lower-fma.f64N/A
distribute-neg-inN/A
metadata-evalN/A
unsub-negN/A
lower--.f64N/A
lower-log.f64N/A
+-commutativeN/A
lower-+.f6486.0
Applied rewrites86.0%
(FPCore (x y z) :precision binary64 (if (<= y 2.9e+21) (- (fma -0.5 (log y) x) z) (- (fma (- y) (log y) y) z)))
double code(double x, double y, double z) {
double tmp;
if (y <= 2.9e+21) {
tmp = fma(-0.5, log(y), x) - z;
} else {
tmp = fma(-y, log(y), y) - z;
}
return tmp;
}
function code(x, y, z) tmp = 0.0 if (y <= 2.9e+21) tmp = Float64(fma(-0.5, log(y), x) - z); else tmp = Float64(fma(Float64(-y), log(y), y) - z); end return tmp end
code[x_, y_, z_] := If[LessEqual[y, 2.9e+21], N[(N[(-0.5 * N[Log[y], $MachinePrecision] + x), $MachinePrecision] - z), $MachinePrecision], N[(N[((-y) * N[Log[y], $MachinePrecision] + y), $MachinePrecision] - z), $MachinePrecision]]
\begin{array}{l}
\\
\begin{array}{l}
\mathbf{if}\;y \leq 2.9 \cdot 10^{+21}:\\
\;\;\;\;\mathsf{fma}\left(-0.5, \log y, x\right) - z\\
\mathbf{else}:\\
\;\;\;\;\mathsf{fma}\left(-y, \log y, y\right) - z\\
\end{array}
\end{array}
if y < 2.9e21Initial program 100.0%
Taylor expanded in y around 0
+-commutativeN/A
associate--r+N/A
lower--.f64N/A
sub-negN/A
+-commutativeN/A
distribute-lft-neg-inN/A
metadata-evalN/A
lower-fma.f64N/A
lower-log.f6499.3
Applied rewrites99.3%
if 2.9e21 < y Initial program 99.8%
Taylor expanded in x around 0
sub-negN/A
+-commutativeN/A
*-commutativeN/A
distribute-lft-neg-inN/A
lower-fma.f64N/A
distribute-neg-inN/A
metadata-evalN/A
unsub-negN/A
lower--.f64N/A
lower-log.f6480.5
Applied rewrites80.5%
Taylor expanded in y around inf
Applied rewrites80.5%
(FPCore (x y z) :precision binary64 (if (<= y 1.9e+165) (- (fma -0.5 (log y) x) z) (* (- 1.0 (log y)) y)))
double code(double x, double y, double z) {
double tmp;
if (y <= 1.9e+165) {
tmp = fma(-0.5, log(y), x) - z;
} else {
tmp = (1.0 - log(y)) * y;
}
return tmp;
}
function code(x, y, z) tmp = 0.0 if (y <= 1.9e+165) tmp = Float64(fma(-0.5, log(y), x) - z); else tmp = Float64(Float64(1.0 - log(y)) * y); end return tmp end
code[x_, y_, z_] := If[LessEqual[y, 1.9e+165], N[(N[(-0.5 * N[Log[y], $MachinePrecision] + x), $MachinePrecision] - z), $MachinePrecision], N[(N[(1.0 - N[Log[y], $MachinePrecision]), $MachinePrecision] * y), $MachinePrecision]]
\begin{array}{l}
\\
\begin{array}{l}
\mathbf{if}\;y \leq 1.9 \cdot 10^{+165}:\\
\;\;\;\;\mathsf{fma}\left(-0.5, \log y, x\right) - z\\
\mathbf{else}:\\
\;\;\;\;\left(1 - \log y\right) \cdot y\\
\end{array}
\end{array}
if y < 1.89999999999999995e165Initial program 99.9%
Taylor expanded in y around 0
+-commutativeN/A
associate--r+N/A
lower--.f64N/A
sub-negN/A
+-commutativeN/A
distribute-lft-neg-inN/A
metadata-evalN/A
lower-fma.f64N/A
lower-log.f6485.0
Applied rewrites85.0%
if 1.89999999999999995e165 < y Initial program 99.7%
Taylor expanded in y around inf
*-commutativeN/A
mul-1-negN/A
log-recN/A
remove-double-negN/A
lower-*.f64N/A
lower--.f64N/A
lower-log.f6483.9
Applied rewrites83.9%
(FPCore (x y z) :precision binary64 (- (+ (* 1.0 x) y) z))
double code(double x, double y, double z) {
return ((1.0 * x) + y) - z;
}
real(8) function code(x, y, z)
real(8), intent (in) :: x
real(8), intent (in) :: y
real(8), intent (in) :: z
code = ((1.0d0 * x) + y) - z
end function
public static double code(double x, double y, double z) {
return ((1.0 * x) + y) - z;
}
def code(x, y, z): return ((1.0 * x) + y) - z
function code(x, y, z) return Float64(Float64(Float64(1.0 * x) + y) - z) end
function tmp = code(x, y, z) tmp = ((1.0 * x) + y) - z; end
code[x_, y_, z_] := N[(N[(N[(1.0 * x), $MachinePrecision] + y), $MachinePrecision] - z), $MachinePrecision]
\begin{array}{l}
\\
\left(1 \cdot x + y\right) - z
\end{array}
Initial program 99.9%
lift-*.f64N/A
*-commutativeN/A
lift-+.f64N/A
flip3-+N/A
clear-numN/A
un-div-invN/A
lower-/.f64N/A
clear-numN/A
flip3-+N/A
lift-+.f64N/A
lower-/.f6499.8
lift-+.f64N/A
+-commutativeN/A
lower-+.f6499.8
Applied rewrites99.8%
Taylor expanded in y around inf
mul-1-negN/A
*-commutativeN/A
distribute-lft-neg-inN/A
log-recN/A
remove-double-negN/A
lower-*.f64N/A
lower-log.f6487.4
Applied rewrites87.4%
Taylor expanded in x around inf
*-commutativeN/A
lower-*.f64N/A
+-commutativeN/A
mul-1-negN/A
associate-/l*N/A
*-commutativeN/A
distribute-lft-neg-inN/A
lower-fma.f64N/A
distribute-neg-fracN/A
lower-/.f64N/A
distribute-neg-inN/A
metadata-evalN/A
unsub-negN/A
lower--.f64N/A
lower-log.f6486.6
Applied rewrites86.6%
Taylor expanded in x around inf
Applied rewrites57.3%
(FPCore (x y z) :precision binary64 (- z))
double code(double x, double y, double z) {
return -z;
}
real(8) function code(x, y, z)
real(8), intent (in) :: x
real(8), intent (in) :: y
real(8), intent (in) :: z
code = -z
end function
public static double code(double x, double y, double z) {
return -z;
}
def code(x, y, z): return -z
function code(x, y, z) return Float64(-z) end
function tmp = code(x, y, z) tmp = -z; end
code[x_, y_, z_] := (-z)
\begin{array}{l}
\\
-z
\end{array}
Initial program 99.9%
Taylor expanded in z around inf
mul-1-negN/A
lower-neg.f6431.2
Applied rewrites31.2%
(FPCore (x y z) :precision binary64 (- (- (+ y x) z) (* (+ y 0.5) (log y))))
double code(double x, double y, double z) {
return ((y + x) - z) - ((y + 0.5) * log(y));
}
real(8) function code(x, y, z)
real(8), intent (in) :: x
real(8), intent (in) :: y
real(8), intent (in) :: z
code = ((y + x) - z) - ((y + 0.5d0) * log(y))
end function
public static double code(double x, double y, double z) {
return ((y + x) - z) - ((y + 0.5) * Math.log(y));
}
def code(x, y, z): return ((y + x) - z) - ((y + 0.5) * math.log(y))
function code(x, y, z) return Float64(Float64(Float64(y + x) - z) - Float64(Float64(y + 0.5) * log(y))) end
function tmp = code(x, y, z) tmp = ((y + x) - z) - ((y + 0.5) * log(y)); end
code[x_, y_, z_] := N[(N[(N[(y + x), $MachinePrecision] - z), $MachinePrecision] - N[(N[(y + 0.5), $MachinePrecision] * N[Log[y], $MachinePrecision]), $MachinePrecision]), $MachinePrecision]
\begin{array}{l}
\\
\left(\left(y + x\right) - z\right) - \left(y + 0.5\right) \cdot \log y
\end{array}
herbie shell --seed 2024285
(FPCore (x y z)
:name "Numeric.SpecFunctions:stirlingError from math-functions-0.1.5.2"
:precision binary64
:alt
(! :herbie-platform default (- (- (+ y x) z) (* (+ y 1/2) (log y))))
(- (+ (- x (* (+ y 0.5) (log y))) y) z))