mirror of https://github.com/mkerrisk/man-pages
116 lines
2.4 KiB
Groff
116 lines
2.4 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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.\"
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.TH LGAMMA 3 2007-07-26 "" "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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.BR lgammaf (),
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.BR lgammal ():
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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 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 this sign via the parameter
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.IR signp .
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.PP
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For non-positive integer values of \fIx\fP,
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.BR lgamma ()
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returns
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.BR HUGE_VAL ,
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sets \fIerrno\fP to
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.B ERANGE
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and raises the zero divide exception.
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(Similarly,
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.BR lgammaf ()
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returns
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.B HUGE_VALF
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and
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.BR lgammal ()
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returns
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.BR HUGE_VALL .)
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.SH ERRORS
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In order to check for errors, set
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.I errno
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to zero and call
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.I feclearexcept(FE_ALL_EXCEPT)
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before calling these functions.
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On return, if
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.I errno
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is nonzero or
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.I fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
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is nonzero, an error has occurred.
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.LP
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A range error occurs if
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.I x
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is too large.
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A pole error occurs if
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.I x
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is a negative integer or zero.
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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 "SEE ALSO"
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.BR tgamma (3)
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