mirror of https://github.com/mkerrisk/man-pages
160 lines
3.4 KiB
Groff
160 lines
3.4 KiB
Groff
.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
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.\" Distributed under GPL
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.\" based on glibc infopages
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.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\"
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.TH LGAMMA 3 2008-08-05 "" "Linux Programmer's Manual"
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.SH NAME
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lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam \-
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log gamma function
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.SH SYNOPSIS
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.nf
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.B #include <math.h>
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.sp
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.BI "double lgamma(double " x );
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.br
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.BI "float lgammaf(float " x );
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.br
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.BI "long double lgammal(long double " x );
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.sp
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.BI "double lgamma_r(double " x ", int *" signp );
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.br
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.BI "float lgammaf_r(float " x ", int *" signp );
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.br
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.BI "long double lgammal_r(long double " x ", int *" signp );
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.sp
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.BI "extern int " signgam ;
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.fi
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.sp
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Link with \fI\-lm\fP.
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.ad l
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.BR lgamma ():
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_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE; or
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.I cc\ -std=c99
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.br
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.BR lgammaf (),
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.BR lgammal ():
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_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
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.I cc\ -std=c99
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.br
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.BR lgamma_r (),
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.BR lgammaf_r (),
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.BR lgammal_r ():
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_BSD_SOURCE || _SVID_SOURCE
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.br
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.IR signgam :
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_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE
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.ad b
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.SH DESCRIPTION
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For the definition of the Gamma function, see
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.BR tgamma (3).
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.PP
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The
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.BR lgamma ()
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function returns the natural logarithm of
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the absolute value of the Gamma function.
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The sign of the Gamma function is returned in the
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external integer \fIsigngam\fP declared in
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.IR <math.h> .
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It is 1 when the Gamma function is positive or zero, \-1
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when it is negative.
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.PP
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Since using a constant location
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.I signgam
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is not thread-safe, the functions
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.BR lgamma_r ()
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etc. have
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been introduced; they return the sign via the argument
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.IR signp .
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.SH RETURN VALUE
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On success, these functions return the natural logarithm of Gamma(x).
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If
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.I x
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is a NaN, a NaN is returned.
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If
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.I x
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is 1 or 2, +0 is returned.
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If
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.I x
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is positive infinity or negative infinity,
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positive infinity is returned.
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If
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.I x
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is a non-positive integer,
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a pole error occurs,
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and the functions return
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.RB + HUGE_VAL ,
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.RB + HUGE_VALF ,
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or
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.RB + HUGE_VALL ,
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respectively.
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If the result overflows,
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a range error occurs,
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.\" e.g., lgamma(DBL_MAX)
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and the functions return
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.BR HUGE_VAL ,
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.BR HUGE_VALF ,
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or
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.BR HUGE_VALL ,
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respectively, with the correct mathematical sign.
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.SH ERRORS
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See
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.BR math_error (7)
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for information on how to determine whether an error has occurred
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when calling these functions.
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.PP
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The following errors can occur:
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.TP
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Pole error: \fIx\fP is a non-positive integer
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.I errno
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is set to
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.\" FIXME . glibc 2.8 gives EDOM!
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.BR ERANGE
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(but see BUGS).
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A divide-by-zero floating-point exception
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.RB ( FE_DIVBYZERO )
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is raised.
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.TP
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Range error: result overflow
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.I errno
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is set to
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.BR ERANGE .
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An overflow floating-point exception
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.RB ( FE_OVERFLOW )
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is raised.
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.\" glibc (as at 2.8) also supports an inexact
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.\" exception for various cases.
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.SH "CONFORMING TO"
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The
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.BR lgamma ()
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functions are specified in C99 and POSIX.1-2001.
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.I signgam
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is specified in POSIX.1-2001, but not in C99.
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The
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.BR lgamma_r ()
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functions are non-standard, but present on several other systems.
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.SH BUGS
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For a pole error,
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.\"
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.\" FIXME . this is as at glibc 2.8; check later if this bug is fixed
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.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6777
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.I errno
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is set to
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.BR EDOM ;
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POSIX.1 says it should be set to
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.BR ERANGE .
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.SH "SEE ALSO"
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.BR tgamma (3)
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