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138 lines
3.1 KiB
Groff
138 lines
3.1 KiB
Groff
.\" Copyright (c) 2008-2010 David Schultz <das@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd June 3, 2013
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.Dt LOG 3
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.Os
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.Sh NAME
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.Nm log ,
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.Nm logf ,
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.Nm logl ,
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.Nm log10 ,
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.Nm log10f ,
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.Nm log10l ,
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.Nm log2 ,
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.Nm log2f ,
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.Nm log2l ,
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.Nm log1p ,
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.Nm log1pf ,
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.Nm log1pl
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.Nd logarithm functions
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.Sh LIBRARY
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.Lb libm
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.Sh SYNOPSIS
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.In math.h
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.Ft double
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.Fn log "double x"
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.Ft float
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.Fn logf "float x"
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.Ft long double
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.Fn logl "long double x"
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.Ft double
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.Fn log10 "double x"
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.Ft float
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.Fn log10f "float x"
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.Ft long double
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.Fn log10l "long double x"
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.Ft double
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.Fn log2 "double x"
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.Ft float
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.Fn log2f "float x"
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.Ft long double
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.Fn log2l "long double x"
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.Ft double
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.Fn log1p "double x"
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.Ft float
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.Fn log1pf "float x"
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.Ft long double
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.Fn log1pl "long double x"
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.Sh DESCRIPTION
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The
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.Fn log ,
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.Fn logf ,
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and
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.Fn logl
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functions compute the natural logarithm of
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.Fa x .
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.Pp
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The
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.Fn log10 ,
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.Fn log10f ,
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and
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.Fn log10l
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functions compute the logarithm base 10 of
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.Fa x ,
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while
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.Fn log2 ,
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.Fn log2f ,
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and
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.Fn log2l
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compute the logarithm base 2 of
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.Fa x .
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.Pp
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The
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.Fn log1p ,
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.Fn log1pf ,
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and
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.Fn log1pl
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functions compute the natural logarithm of
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.No "1 + x" .
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Computing the natural logarithm as
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.Li log1p(x)
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is more accurate than computing it as
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.Li log(1 + x)
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when
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.Fa x
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is close to zero.
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.Sh RETURN VALUES
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These functions return the requested logarithm; the logarithm of 1 is +0.
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An attempt to take the logarithm of \*(Pm0 results in a divide-by-zero
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exception, and -\*(If is returned.
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Otherwise, attempting to take the logarithm of a negative number
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results in an invalid exception and a return value of \*(Na.
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.Sh SEE ALSO
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.Xr exp 3 ,
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.Xr ilogb 3 ,
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.Xr math 3 ,
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.Xr pow 3
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.Sh STANDARDS
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The
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.Fn log ,
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.Fn logf ,
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.Fn logl ,
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.Fn log10 ,
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.Fn log10f ,
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.Fn log10l ,
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.Fn log2 ,
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.Fn log2f ,
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.Fn log2l ,
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.Fn log1p ,
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.Fn log1pf ,
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and
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.Fn log1pl
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functions conform to
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.St -isoC-99 .
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