mirror of https://github.com/mkerrisk/man-pages
65 lines
1.8 KiB
Groff
65 lines
1.8 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 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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Compile with \-std=c99; link with \-lm.
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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 \fBlgamma()\fP 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 \fBlgamma_r()\fP 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 nonpositive integer values of \fIx\fP, \fBlgamma()\fP returns HUGE_VAL,
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sets \fIerrno\fP to ERANGE and raises the zero divide exception.
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(Similarly, \fBlgammaf()\fP returns HUGE_VALF and \fBlgammal()\fP returns
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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. 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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C99, SVID 3, BSD 4.3
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.SH "SEE ALSO"
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.BR tgamma (3)
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