log_falling_factorial() [4/8]

template<typename T1 , typename T2 , require_all_arithmetic_t< T1, T2 > * = nullptr>

return_type_t< T1, T2 > stan::math::log_falling_factorial ( const T1  x, const T2  n  )

inline

Return the natural log of the falling factorial of the specified arguments.

\[ \mbox{log\_falling\_factorial}(x, n) = \begin{cases} \textrm{error} & \mbox{if } x \leq 0\\ \ln (x)_n & \mbox{if } x > 0 \textrm{ and } -\infty \leq n \leq \infty \\[6pt] \textrm{NaN} & \mbox{if } x = \textrm{NaN or } n = \textrm{NaN} \end{cases} \]

\[ \frac{\partial\, \mbox{log\_falling\_factorial}(x, n)}{\partial x} = \begin{cases} \textrm{error} & \mbox{if } x \leq 0\\ \Psi(x) & \mbox{if } x > 0 \textrm{ and } -\infty \leq n \leq \infty \\[6pt] \textrm{NaN} & \mbox{if } x = \textrm{NaN or } n = \textrm{NaN} \end{cases} \]

\[ \frac{\partial\, \mbox{log\_falling\_factorial}(x, n)}{\partial n} = \begin{cases} \textrm{error} & \mbox{if } x \leq 0\\ -\Psi(n) & \mbox{if } x > 0 \textrm{ and } -\infty \leq n \leq \infty \\[6pt] \textrm{NaN} & \mbox{if } x = \textrm{NaN or } n = \textrm{NaN} \end{cases} \]

Template Parameters

T1	type of first argument
T2	type of second argument

Parameters

[in]	x	First argument
[in]	n	Second argument

Returns

log of falling factorial of arguments

Exceptions

std::domain_error

if the first argument is not positive

Definition at line 55 of file log_falling_factorial.hpp.