2004-11-03 13:51:07 +00:00
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.\" 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 2002-08-10 "" "Linux Programmer's Manual"
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.SH NAME
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lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r \- 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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.fi
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.sp
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2007-05-21 09:56:00 +00:00
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Compile with \fI\-std=c99\fP; link with \fI\-lm\fP.
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2004-11-03 13:51:07 +00:00
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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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2007-05-12 09:06:04 +00:00
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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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2004-11-03 13:51:07 +00:00
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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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2004-11-03 13:51:07 +00:00
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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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2007-05-12 09:06:04 +00:00
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For non-positive integer values of \fIx\fP,
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.BR lgamma ()
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2007-06-22 19:42:52 +00:00
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returns
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.BR HUGE_VAL ,
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2007-06-22 18:09:13 +00:00
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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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2007-06-22 19:42:52 +00:00
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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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2007-04-12 22:42:49 +00:00
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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 non-zero or
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.I fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
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is non-zero, an error has occurred.
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.LP
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A range error occurs if x is too large.
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A pole error occurs if x is a negative integer or zero.
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.SH "CONFORMING TO"
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2006-08-03 13:57:30 +00:00
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C99, SVr4, 4.3BSD
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.SH "SEE ALSO"
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.BR tgamma (3)
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