1LGAMMA(3) Linux Programmer's Manual LGAMMA(3)
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6 lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r - log gamma
7 function
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10 #include <math.h>
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12 double lgamma(double x);
13 float lgammaf(float x);
14 long double lgammal(long double x);
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16 double lgamma_r(double x, int *signp);
17 float lgammaf_r(float x, int *signp);
18 long double lgammal_r(long double x, int *signp);
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20 Compile with -std=c99; link with -lm.
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23 For the definition of the Gamma function, see tgamma(3).
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25 The lgamma() function returns the natural logarithm of the absolute
26 value of the Gamma function. The sign of the Gamma function is
27 returned in the external integer signgam declared in <math.h>. It is 1
28 when the Gamma function is positive or zero, -1 when it is negative.
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30 Since using a constant location signgam is not thread-safe, the func‐
31 tions lgamma_r() etc. have been introduced; they return this sign via
32 the parameter signp.
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34 For non-positive integer values of x, lgamma() returns HUGE_VAL, sets
35 errno to ERANGE and raises the zero divide exception. (Similarly,
36 lgammaf() returns HUGE_VALF and lgammal() returns HUGE_VALL.)
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39 In order to check for errors, set errno to zero and call feclearex‐
40 cept(FE_ALL_EXCEPT) before calling these functions. On return, if errno
41 is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW |
42 FE_UNDERFLOW) is non-zero, an error has occurred.
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44 A range error occurs if x is too large. A pole error occurs if x is a
45 negative integer or zero.
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48 C99, SVr4, 4.3BSD
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51 tgamma(3)
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55 2002-08-10 LGAMMA(3)