
(FPCore (c_p c_n t s)
:precision binary64
(let* ((t_1 (/ 1.0 (+ 1.0 (exp (- t))))) (t_2 (/ 1.0 (+ 1.0 (exp (- s))))))
(/
(* (pow t_2 c_p) (pow (- 1.0 t_2) c_n))
(* (pow t_1 c_p) (pow (- 1.0 t_1) c_n)))))
double code(double c_p, double c_n, double t, double s) {
double t_1 = 1.0 / (1.0 + exp(-t));
double t_2 = 1.0 / (1.0 + exp(-s));
return (pow(t_2, c_p) * pow((1.0 - t_2), c_n)) / (pow(t_1, c_p) * pow((1.0 - t_1), c_n));
}
real(8) function code(c_p, c_n, t, s)
real(8), intent (in) :: c_p
real(8), intent (in) :: c_n
real(8), intent (in) :: t
real(8), intent (in) :: s
real(8) :: t_1
real(8) :: t_2
t_1 = 1.0d0 / (1.0d0 + exp(-t))
t_2 = 1.0d0 / (1.0d0 + exp(-s))
code = ((t_2 ** c_p) * ((1.0d0 - t_2) ** c_n)) / ((t_1 ** c_p) * ((1.0d0 - t_1) ** c_n))
end function
public static double code(double c_p, double c_n, double t, double s) {
double t_1 = 1.0 / (1.0 + Math.exp(-t));
double t_2 = 1.0 / (1.0 + Math.exp(-s));
return (Math.pow(t_2, c_p) * Math.pow((1.0 - t_2), c_n)) / (Math.pow(t_1, c_p) * Math.pow((1.0 - t_1), c_n));
}
def code(c_p, c_n, t, s): t_1 = 1.0 / (1.0 + math.exp(-t)) t_2 = 1.0 / (1.0 + math.exp(-s)) return (math.pow(t_2, c_p) * math.pow((1.0 - t_2), c_n)) / (math.pow(t_1, c_p) * math.pow((1.0 - t_1), c_n))
function code(c_p, c_n, t, s) t_1 = Float64(1.0 / Float64(1.0 + exp(Float64(-t)))) t_2 = Float64(1.0 / Float64(1.0 + exp(Float64(-s)))) return Float64(Float64((t_2 ^ c_p) * (Float64(1.0 - t_2) ^ c_n)) / Float64((t_1 ^ c_p) * (Float64(1.0 - t_1) ^ c_n))) end
function tmp = code(c_p, c_n, t, s) t_1 = 1.0 / (1.0 + exp(-t)); t_2 = 1.0 / (1.0 + exp(-s)); tmp = ((t_2 ^ c_p) * ((1.0 - t_2) ^ c_n)) / ((t_1 ^ c_p) * ((1.0 - t_1) ^ c_n)); end
code[c$95$p_, c$95$n_, t_, s_] := Block[{t$95$1 = N[(1.0 / N[(1.0 + N[Exp[(-t)], $MachinePrecision]), $MachinePrecision]), $MachinePrecision]}, Block[{t$95$2 = N[(1.0 / N[(1.0 + N[Exp[(-s)], $MachinePrecision]), $MachinePrecision]), $MachinePrecision]}, N[(N[(N[Power[t$95$2, c$95$p], $MachinePrecision] * N[Power[N[(1.0 - t$95$2), $MachinePrecision], c$95$n], $MachinePrecision]), $MachinePrecision] / N[(N[Power[t$95$1, c$95$p], $MachinePrecision] * N[Power[N[(1.0 - t$95$1), $MachinePrecision], c$95$n], $MachinePrecision]), $MachinePrecision]), $MachinePrecision]]]
\begin{array}{l}
\\
\begin{array}{l}
t_1 := \frac{1}{1 + e^{-t}}\\
t_2 := \frac{1}{1 + e^{-s}}\\
\frac{{t\_2}^{c\_p} \cdot {\left(1 - t\_2\right)}^{c\_n}}{{t\_1}^{c\_p} \cdot {\left(1 - t\_1\right)}^{c\_n}}
\end{array}
\end{array}
Sampling outcomes in binary64 precision:
Herbie found 4 alternatives:
| Alternative | Accuracy | Speedup |
|---|
(FPCore (c_p c_n t s)
:precision binary64
(let* ((t_1 (/ 1.0 (+ 1.0 (exp (- t))))) (t_2 (/ 1.0 (+ 1.0 (exp (- s))))))
(/
(* (pow t_2 c_p) (pow (- 1.0 t_2) c_n))
(* (pow t_1 c_p) (pow (- 1.0 t_1) c_n)))))
double code(double c_p, double c_n, double t, double s) {
double t_1 = 1.0 / (1.0 + exp(-t));
double t_2 = 1.0 / (1.0 + exp(-s));
return (pow(t_2, c_p) * pow((1.0 - t_2), c_n)) / (pow(t_1, c_p) * pow((1.0 - t_1), c_n));
}
real(8) function code(c_p, c_n, t, s)
real(8), intent (in) :: c_p
real(8), intent (in) :: c_n
real(8), intent (in) :: t
real(8), intent (in) :: s
real(8) :: t_1
real(8) :: t_2
t_1 = 1.0d0 / (1.0d0 + exp(-t))
t_2 = 1.0d0 / (1.0d0 + exp(-s))
code = ((t_2 ** c_p) * ((1.0d0 - t_2) ** c_n)) / ((t_1 ** c_p) * ((1.0d0 - t_1) ** c_n))
end function
public static double code(double c_p, double c_n, double t, double s) {
double t_1 = 1.0 / (1.0 + Math.exp(-t));
double t_2 = 1.0 / (1.0 + Math.exp(-s));
return (Math.pow(t_2, c_p) * Math.pow((1.0 - t_2), c_n)) / (Math.pow(t_1, c_p) * Math.pow((1.0 - t_1), c_n));
}
def code(c_p, c_n, t, s): t_1 = 1.0 / (1.0 + math.exp(-t)) t_2 = 1.0 / (1.0 + math.exp(-s)) return (math.pow(t_2, c_p) * math.pow((1.0 - t_2), c_n)) / (math.pow(t_1, c_p) * math.pow((1.0 - t_1), c_n))
function code(c_p, c_n, t, s) t_1 = Float64(1.0 / Float64(1.0 + exp(Float64(-t)))) t_2 = Float64(1.0 / Float64(1.0 + exp(Float64(-s)))) return Float64(Float64((t_2 ^ c_p) * (Float64(1.0 - t_2) ^ c_n)) / Float64((t_1 ^ c_p) * (Float64(1.0 - t_1) ^ c_n))) end
function tmp = code(c_p, c_n, t, s) t_1 = 1.0 / (1.0 + exp(-t)); t_2 = 1.0 / (1.0 + exp(-s)); tmp = ((t_2 ^ c_p) * ((1.0 - t_2) ^ c_n)) / ((t_1 ^ c_p) * ((1.0 - t_1) ^ c_n)); end
code[c$95$p_, c$95$n_, t_, s_] := Block[{t$95$1 = N[(1.0 / N[(1.0 + N[Exp[(-t)], $MachinePrecision]), $MachinePrecision]), $MachinePrecision]}, Block[{t$95$2 = N[(1.0 / N[(1.0 + N[Exp[(-s)], $MachinePrecision]), $MachinePrecision]), $MachinePrecision]}, N[(N[(N[Power[t$95$2, c$95$p], $MachinePrecision] * N[Power[N[(1.0 - t$95$2), $MachinePrecision], c$95$n], $MachinePrecision]), $MachinePrecision] / N[(N[Power[t$95$1, c$95$p], $MachinePrecision] * N[Power[N[(1.0 - t$95$1), $MachinePrecision], c$95$n], $MachinePrecision]), $MachinePrecision]), $MachinePrecision]]]
\begin{array}{l}
\\
\begin{array}{l}
t_1 := \frac{1}{1 + e^{-t}}\\
t_2 := \frac{1}{1 + e^{-s}}\\
\frac{{t\_2}^{c\_p} \cdot {\left(1 - t\_2\right)}^{c\_n}}{{t\_1}^{c\_p} \cdot {\left(1 - t\_1\right)}^{c\_n}}
\end{array}
\end{array}
(FPCore (c_p c_n t s)
:precision binary64
(let* ((t_1 (+ (exp (- s)) 1.0)))
(if (<= (- s) -1e-286)
(/
(pow (- 1.0 (pow t_1 -1.0)) c_n)
(pow (- 1.0 (pow (+ (exp (- t)) 1.0) -1.0)) c_n))
(pow (* t_1 0.5) (- c_p)))))
double code(double c_p, double c_n, double t, double s) {
double t_1 = exp(-s) + 1.0;
double tmp;
if (-s <= -1e-286) {
tmp = pow((1.0 - pow(t_1, -1.0)), c_n) / pow((1.0 - pow((exp(-t) + 1.0), -1.0)), c_n);
} else {
tmp = pow((t_1 * 0.5), -c_p);
}
return tmp;
}
real(8) function code(c_p, c_n, t, s)
real(8), intent (in) :: c_p
real(8), intent (in) :: c_n
real(8), intent (in) :: t
real(8), intent (in) :: s
real(8) :: t_1
real(8) :: tmp
t_1 = exp(-s) + 1.0d0
if (-s <= (-1d-286)) then
tmp = ((1.0d0 - (t_1 ** (-1.0d0))) ** c_n) / ((1.0d0 - ((exp(-t) + 1.0d0) ** (-1.0d0))) ** c_n)
else
tmp = (t_1 * 0.5d0) ** -c_p
end if
code = tmp
end function
public static double code(double c_p, double c_n, double t, double s) {
double t_1 = Math.exp(-s) + 1.0;
double tmp;
if (-s <= -1e-286) {
tmp = Math.pow((1.0 - Math.pow(t_1, -1.0)), c_n) / Math.pow((1.0 - Math.pow((Math.exp(-t) + 1.0), -1.0)), c_n);
} else {
tmp = Math.pow((t_1 * 0.5), -c_p);
}
return tmp;
}
def code(c_p, c_n, t, s): t_1 = math.exp(-s) + 1.0 tmp = 0 if -s <= -1e-286: tmp = math.pow((1.0 - math.pow(t_1, -1.0)), c_n) / math.pow((1.0 - math.pow((math.exp(-t) + 1.0), -1.0)), c_n) else: tmp = math.pow((t_1 * 0.5), -c_p) return tmp
function code(c_p, c_n, t, s) t_1 = Float64(exp(Float64(-s)) + 1.0) tmp = 0.0 if (Float64(-s) <= -1e-286) tmp = Float64((Float64(1.0 - (t_1 ^ -1.0)) ^ c_n) / (Float64(1.0 - (Float64(exp(Float64(-t)) + 1.0) ^ -1.0)) ^ c_n)); else tmp = Float64(t_1 * 0.5) ^ Float64(-c_p); end return tmp end
function tmp_2 = code(c_p, c_n, t, s) t_1 = exp(-s) + 1.0; tmp = 0.0; if (-s <= -1e-286) tmp = ((1.0 - (t_1 ^ -1.0)) ^ c_n) / ((1.0 - ((exp(-t) + 1.0) ^ -1.0)) ^ c_n); else tmp = (t_1 * 0.5) ^ -c_p; end tmp_2 = tmp; end
code[c$95$p_, c$95$n_, t_, s_] := Block[{t$95$1 = N[(N[Exp[(-s)], $MachinePrecision] + 1.0), $MachinePrecision]}, If[LessEqual[(-s), -1e-286], N[(N[Power[N[(1.0 - N[Power[t$95$1, -1.0], $MachinePrecision]), $MachinePrecision], c$95$n], $MachinePrecision] / N[Power[N[(1.0 - N[Power[N[(N[Exp[(-t)], $MachinePrecision] + 1.0), $MachinePrecision], -1.0], $MachinePrecision]), $MachinePrecision], c$95$n], $MachinePrecision]), $MachinePrecision], N[Power[N[(t$95$1 * 0.5), $MachinePrecision], (-c$95$p)], $MachinePrecision]]]
\begin{array}{l}
\\
\begin{array}{l}
t_1 := e^{-s} + 1\\
\mathbf{if}\;-s \leq -1 \cdot 10^{-286}:\\
\;\;\;\;\frac{{\left(1 - {t\_1}^{-1}\right)}^{c\_n}}{{\left(1 - {\left(e^{-t} + 1\right)}^{-1}\right)}^{c\_n}}\\
\mathbf{else}:\\
\;\;\;\;{\left(t\_1 \cdot 0.5\right)}^{\left(-c\_p\right)}\\
\end{array}
\end{array}
if (neg.f64 s) < -1.00000000000000005e-286Initial program 95.0%
Taylor expanded in c_p around 0
lower-/.f64N/A
lower-pow.f64N/A
lower--.f64N/A
lower-/.f64N/A
+-commutativeN/A
lower-+.f64N/A
lower-exp.f64N/A
lower-neg.f64N/A
lower-pow.f64N/A
Applied rewrites100.0%
if -1.00000000000000005e-286 < (neg.f64 s) Initial program 92.8%
Taylor expanded in c_n around 0
lower-/.f64N/A
lower-pow.f64N/A
lower-/.f64N/A
+-commutativeN/A
lower-+.f64N/A
lower-exp.f64N/A
lower-neg.f64N/A
lower-pow.f64N/A
lower-/.f64N/A
+-commutativeN/A
lower-+.f64N/A
lower-exp.f64N/A
lower-neg.f6496.4
Applied rewrites96.4%
Taylor expanded in t around 0
Applied rewrites97.1%
Applied rewrites97.1%
Applied rewrites97.8%
Final simplification98.8%
(FPCore (c_p c_n t s) :precision binary64 (if (<= t -1e-38) (/ (pow 0.5 c_n) (pow (- 1.0 (pow (+ (exp (- t)) 1.0) -1.0)) c_n)) (pow (* (+ (exp (- s)) 1.0) 0.5) (- c_p))))
double code(double c_p, double c_n, double t, double s) {
double tmp;
if (t <= -1e-38) {
tmp = pow(0.5, c_n) / pow((1.0 - pow((exp(-t) + 1.0), -1.0)), c_n);
} else {
tmp = pow(((exp(-s) + 1.0) * 0.5), -c_p);
}
return tmp;
}
real(8) function code(c_p, c_n, t, s)
real(8), intent (in) :: c_p
real(8), intent (in) :: c_n
real(8), intent (in) :: t
real(8), intent (in) :: s
real(8) :: tmp
if (t <= (-1d-38)) then
tmp = (0.5d0 ** c_n) / ((1.0d0 - ((exp(-t) + 1.0d0) ** (-1.0d0))) ** c_n)
else
tmp = ((exp(-s) + 1.0d0) * 0.5d0) ** -c_p
end if
code = tmp
end function
public static double code(double c_p, double c_n, double t, double s) {
double tmp;
if (t <= -1e-38) {
tmp = Math.pow(0.5, c_n) / Math.pow((1.0 - Math.pow((Math.exp(-t) + 1.0), -1.0)), c_n);
} else {
tmp = Math.pow(((Math.exp(-s) + 1.0) * 0.5), -c_p);
}
return tmp;
}
def code(c_p, c_n, t, s): tmp = 0 if t <= -1e-38: tmp = math.pow(0.5, c_n) / math.pow((1.0 - math.pow((math.exp(-t) + 1.0), -1.0)), c_n) else: tmp = math.pow(((math.exp(-s) + 1.0) * 0.5), -c_p) return tmp
function code(c_p, c_n, t, s) tmp = 0.0 if (t <= -1e-38) tmp = Float64((0.5 ^ c_n) / (Float64(1.0 - (Float64(exp(Float64(-t)) + 1.0) ^ -1.0)) ^ c_n)); else tmp = Float64(Float64(exp(Float64(-s)) + 1.0) * 0.5) ^ Float64(-c_p); end return tmp end
function tmp_2 = code(c_p, c_n, t, s) tmp = 0.0; if (t <= -1e-38) tmp = (0.5 ^ c_n) / ((1.0 - ((exp(-t) + 1.0) ^ -1.0)) ^ c_n); else tmp = ((exp(-s) + 1.0) * 0.5) ^ -c_p; end tmp_2 = tmp; end
code[c$95$p_, c$95$n_, t_, s_] := If[LessEqual[t, -1e-38], N[(N[Power[0.5, c$95$n], $MachinePrecision] / N[Power[N[(1.0 - N[Power[N[(N[Exp[(-t)], $MachinePrecision] + 1.0), $MachinePrecision], -1.0], $MachinePrecision]), $MachinePrecision], c$95$n], $MachinePrecision]), $MachinePrecision], N[Power[N[(N[(N[Exp[(-s)], $MachinePrecision] + 1.0), $MachinePrecision] * 0.5), $MachinePrecision], (-c$95$p)], $MachinePrecision]]
\begin{array}{l}
\\
\begin{array}{l}
\mathbf{if}\;t \leq -1 \cdot 10^{-38}:\\
\;\;\;\;\frac{{0.5}^{c\_n}}{{\left(1 - {\left(e^{-t} + 1\right)}^{-1}\right)}^{c\_n}}\\
\mathbf{else}:\\
\;\;\;\;{\left(\left(e^{-s} + 1\right) \cdot 0.5\right)}^{\left(-c\_p\right)}\\
\end{array}
\end{array}
if t < -9.9999999999999996e-39Initial program 65.9%
Taylor expanded in c_p around 0
lower-/.f64N/A
lower-pow.f64N/A
lower--.f64N/A
lower-/.f64N/A
+-commutativeN/A
lower-+.f64N/A
lower-exp.f64N/A
lower-neg.f64N/A
lower-pow.f64N/A
Applied rewrites96.2%
Taylor expanded in s around 0
Applied rewrites96.2%
if -9.9999999999999996e-39 < t Initial program 97.0%
Taylor expanded in c_n around 0
lower-/.f64N/A
lower-pow.f64N/A
lower-/.f64N/A
+-commutativeN/A
lower-+.f64N/A
lower-exp.f64N/A
lower-neg.f64N/A
lower-pow.f64N/A
lower-/.f64N/A
+-commutativeN/A
lower-+.f64N/A
lower-exp.f64N/A
lower-neg.f6497.5
Applied rewrites97.5%
Taylor expanded in t around 0
Applied rewrites97.5%
Applied rewrites97.5%
Applied rewrites97.9%
Final simplification97.7%
(FPCore (c_p c_n t s) :precision binary64 (pow (* (+ (exp (- s)) 1.0) 0.5) (- c_p)))
double code(double c_p, double c_n, double t, double s) {
return pow(((exp(-s) + 1.0) * 0.5), -c_p);
}
real(8) function code(c_p, c_n, t, s)
real(8), intent (in) :: c_p
real(8), intent (in) :: c_n
real(8), intent (in) :: t
real(8), intent (in) :: s
code = ((exp(-s) + 1.0d0) * 0.5d0) ** -c_p
end function
public static double code(double c_p, double c_n, double t, double s) {
return Math.pow(((Math.exp(-s) + 1.0) * 0.5), -c_p);
}
def code(c_p, c_n, t, s): return math.pow(((math.exp(-s) + 1.0) * 0.5), -c_p)
function code(c_p, c_n, t, s) return Float64(Float64(exp(Float64(-s)) + 1.0) * 0.5) ^ Float64(-c_p) end
function tmp = code(c_p, c_n, t, s) tmp = ((exp(-s) + 1.0) * 0.5) ^ -c_p; end
code[c$95$p_, c$95$n_, t_, s_] := N[Power[N[(N[(N[Exp[(-s)], $MachinePrecision] + 1.0), $MachinePrecision] * 0.5), $MachinePrecision], (-c$95$p)], $MachinePrecision]
\begin{array}{l}
\\
{\left(\left(e^{-s} + 1\right) \cdot 0.5\right)}^{\left(-c\_p\right)}
\end{array}
Initial program 93.8%
Taylor expanded in c_n around 0
lower-/.f64N/A
lower-pow.f64N/A
lower-/.f64N/A
+-commutativeN/A
lower-+.f64N/A
lower-exp.f64N/A
lower-neg.f64N/A
lower-pow.f64N/A
lower-/.f64N/A
+-commutativeN/A
lower-+.f64N/A
lower-exp.f64N/A
lower-neg.f6494.6
Applied rewrites94.6%
Taylor expanded in t around 0
Applied rewrites95.6%
Applied rewrites95.6%
Applied rewrites96.0%
(FPCore (c_p c_n t s) :precision binary64 1.0)
double code(double c_p, double c_n, double t, double s) {
return 1.0;
}
real(8) function code(c_p, c_n, t, s)
real(8), intent (in) :: c_p
real(8), intent (in) :: c_n
real(8), intent (in) :: t
real(8), intent (in) :: s
code = 1.0d0
end function
public static double code(double c_p, double c_n, double t, double s) {
return 1.0;
}
def code(c_p, c_n, t, s): return 1.0
function code(c_p, c_n, t, s) return 1.0 end
function tmp = code(c_p, c_n, t, s) tmp = 1.0; end
code[c$95$p_, c$95$n_, t_, s_] := 1.0
\begin{array}{l}
\\
1
\end{array}
Initial program 93.8%
Taylor expanded in c_n around 0
lower-/.f64N/A
lower-pow.f64N/A
lower-/.f64N/A
+-commutativeN/A
lower-+.f64N/A
lower-exp.f64N/A
lower-neg.f64N/A
lower-pow.f64N/A
lower-/.f64N/A
+-commutativeN/A
lower-+.f64N/A
lower-exp.f64N/A
lower-neg.f6494.6
Applied rewrites94.6%
Taylor expanded in c_p around 0
Applied rewrites95.6%
(FPCore (c_p c_n t s) :precision binary64 (* (pow (/ (+ 1.0 (exp (- t))) (+ 1.0 (exp (- s)))) c_p) (pow (/ (+ 1.0 (exp t)) (+ 1.0 (exp s))) c_n)))
double code(double c_p, double c_n, double t, double s) {
return pow(((1.0 + exp(-t)) / (1.0 + exp(-s))), c_p) * pow(((1.0 + exp(t)) / (1.0 + exp(s))), c_n);
}
real(8) function code(c_p, c_n, t, s)
real(8), intent (in) :: c_p
real(8), intent (in) :: c_n
real(8), intent (in) :: t
real(8), intent (in) :: s
code = (((1.0d0 + exp(-t)) / (1.0d0 + exp(-s))) ** c_p) * (((1.0d0 + exp(t)) / (1.0d0 + exp(s))) ** c_n)
end function
public static double code(double c_p, double c_n, double t, double s) {
return Math.pow(((1.0 + Math.exp(-t)) / (1.0 + Math.exp(-s))), c_p) * Math.pow(((1.0 + Math.exp(t)) / (1.0 + Math.exp(s))), c_n);
}
def code(c_p, c_n, t, s): return math.pow(((1.0 + math.exp(-t)) / (1.0 + math.exp(-s))), c_p) * math.pow(((1.0 + math.exp(t)) / (1.0 + math.exp(s))), c_n)
function code(c_p, c_n, t, s) return Float64((Float64(Float64(1.0 + exp(Float64(-t))) / Float64(1.0 + exp(Float64(-s)))) ^ c_p) * (Float64(Float64(1.0 + exp(t)) / Float64(1.0 + exp(s))) ^ c_n)) end
function tmp = code(c_p, c_n, t, s) tmp = (((1.0 + exp(-t)) / (1.0 + exp(-s))) ^ c_p) * (((1.0 + exp(t)) / (1.0 + exp(s))) ^ c_n); end
code[c$95$p_, c$95$n_, t_, s_] := N[(N[Power[N[(N[(1.0 + N[Exp[(-t)], $MachinePrecision]), $MachinePrecision] / N[(1.0 + N[Exp[(-s)], $MachinePrecision]), $MachinePrecision]), $MachinePrecision], c$95$p], $MachinePrecision] * N[Power[N[(N[(1.0 + N[Exp[t], $MachinePrecision]), $MachinePrecision] / N[(1.0 + N[Exp[s], $MachinePrecision]), $MachinePrecision]), $MachinePrecision], c$95$n], $MachinePrecision]), $MachinePrecision]
\begin{array}{l}
\\
{\left(\frac{1 + e^{-t}}{1 + e^{-s}}\right)}^{c\_p} \cdot {\left(\frac{1 + e^{t}}{1 + e^{s}}\right)}^{c\_n}
\end{array}
herbie shell --seed 2024318
(FPCore (c_p c_n t s)
:name "Harley's example"
:precision binary64
:pre (and (< 0.0 c_p) (< 0.0 c_n))
:alt
(! :herbie-platform default (* (pow (/ (+ 1 (exp (- t))) (+ 1 (exp (- s)))) c_p) (pow (/ (+ 1 (exp t)) (+ 1 (exp s))) c_n)))
(/ (* (pow (/ 1.0 (+ 1.0 (exp (- s)))) c_p) (pow (- 1.0 (/ 1.0 (+ 1.0 (exp (- s))))) c_n)) (* (pow (/ 1.0 (+ 1.0 (exp (- t)))) c_p) (pow (- 1.0 (/ 1.0 (+ 1.0 (exp (- t))))) c_n))))