lgamma, lgammaf, lgammal

Determines the natural logarithm of the absolute value of the gamma function of the specified value.

Syntax

double lgamma( double x );
float lgammaf( float x );
long double lgammal( long double x );
#define lgammal(X) // Requires C11 or higher

float lgamma( float x ); //C++ only
long double lgamma( long double x ); //C++ only

Parameters

x
The value to compute.

Return value

If successful, return the natural logarithm of the absolute value of the gamma function of x.

Issue	Return
x = NaN	NaN
x = ±0	+INFINITY
x= negative integer	+INFINITY
±INFINITY	+INFINITY
pole error	+HUGE_VAL, +HUGE_VALF, or +HUGE_VALL
overflow range error	±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL

Errors are reported as specified in _matherr.

Remarks

Because C++ allows overloading, you can call overloads of lgamma that take and return float and long double types. In a C program, unless you're using the <tgmath.h> macro to call this function, lgamma always takes and returns a double.

If you use the <tgmath.h> lgamma() macro, the type of the argument determines which version of the function is selected. See Type-generic math for details.

If x is a rational number, this function returns the logarithm of the factorial of (x - 1).

By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.

Requirements

Function	C header	C++ header
lgamma, lgammaf, lgammal	<math.h>	<cmath>
lgamma macro	<tgmath.h>

For more compatibility information, see Compatibility.

See also

Alphabetical function reference
tgamma, tgammaf, tgammal