tgamma, tgammaf, tgammal
| Defined in header
<math.h>
|
||
| float tgammaf( float arg );
|
(1) | (since C99) |
| double tgamma( double arg );
|
(2) | (since C99) |
| long double tgammal( long double arg );
|
(3) | (since C99) |
| Defined in header
<tgmath.h>
|
||
| #define lgamma( arg )
|
(4) | (since C99) |
arg has type long double, lgammal is called. Otherwise, if arg has integer type or the type double, lgamma is called. Otherwise, lgammaf is called.
Contents |
[edit] Parameters
| arg | - | floating point value |
[edit] Return value
If no errors occur, the value of the gamma function of arg, that is ∫∞
0targ-1
e-t dt, is returned
If a domain error occurs, an implementation-defined value (NaN where supported) is returned.
If a pole error occurs, ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL is returned.
If a range error due to overflow occurs, ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL is returned.
If a range error due to underflow occurs, the correct value (after rounding) is returned.
[edit] Error handling
Errors are reported as specified in math_errhandling
If arg is zero or is an integer less than zero, a pole error or a domain error may occur.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
- If the argument is ±0, ±∞ is returned and FE_DIVBYZERO is raised
- If the argument is a negative integer, NaN is returned and FE_INVALID is raised
- If the argument is -∞, NaN is returned and FE_INVALID is raised
- If the argument is +∞, +∞ is returned.
- If the argument is NaN, NaN is returned
[edit] Notes
If arg is a natural number, tgamma(arg) is the factorial of arg-1. Many implementations calculate the exact integer-domain factorial if the argument is a sufficiently small integer.
For IEEE-compatible type double, overflow happens if 0 < x < 1/DBL_MAX or if x > 171.7
POSIX requires that a pole error occurs if the argument is zero, but a domain error occurs when the argument is a negative integer. It also specifies that in future, domain errors may be replaced by pole errors for negative integer arguments (in which case the return value in those cases would change from NaN to ±∞).
There is a non-standard function named gamma in various implementations, but its definition is inconsistent. For example, glibc and 4.2BSD version of gamma executes lgamma, but 4.4BSD version of gamma executes tgamma.
[edit] Example
#include <stdio.h> #include <math.h> #include <float.h> #include <errno.h> #include <fenv.h> #pragma STDC FENV_ACCESS ON int main(void) { printf("tgamma(10) = %f, 9!=%f\n", tgamma(10), 2*3*4*5*6*7*8*9.0); printf("tgamma(0.5) = %f, sqrt(pi) = %f\n", sqrt(acos(-1)), tgamma(0.5)); // special values printf("tgamma(+Inf) = %f\n", tgamma(INFINITY)); //error handling errno = 0; feclearexcept(FE_ALL_EXCEPT); printf("tgamma(-1) = %f\n", tgamma(-1)); if(errno == ERANGE) perror(" errno == ERANGE"); else if(errno == EDOM) perror(" errno == EDOM"); if(fetestexcept(FE_DIVBYZERO)) puts(" FE_DIVBYZERO raised"); else if(fetestexcept(FE_INVALID)) puts(" FE_INVALID raised"); }
Possible output:
tgamma(10) = 362880.000000, 9!=362880.000000
tgamma(0.5) = 1.772454, sqrt(pi) = 1.772454
tgamma(+Inf) = inf
tgamma(-1) = nan
errno == EDOM: Numerical argument out of domain
FE_INVALID raised[edit] See also
| (C99)(C99)(C99)
|
computes natural (base-e) logarithm of the gamma function (function) |
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C++ documentation for tgamma
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[edit] External links
Weisstein, Eric W. "Gamma Function." From MathWorld--A Wolfram Web Resource.