qccmath.3

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.TH QCCMATH 3 "QCCPACK" ""
.SH NAME
QccMathMax,
QccMathMin,
QccMathPercent,
QccMathModulus,
QccMathLog2,
QccMathMedian,
QccMathRand,
QccMathRandNormal,
QccMathGaussianDensity,
QccMathLaplacianDensity
\- various math routines
.SH SYNOPSIS
.B #include "libQccPack.h"
.sp
.BI "QccMathMax(" x ", " y )
.br
.BI "QccMathMin(" x ", " y )
.br
.BI "QccMathPercent(" x ", " y )
.br
.BI "QccMathModulus(" x ", " y )
.br
.BI "QccMathLog2(" x )
.br
.BI "QccMathMedian(" a ", " b ", " c )
.br
.B double QccMathRand(void);
.br
.B double QccMathRandNormal(void);
.br
.BI "double QccMathGaussianDensity(double " x ", double " variance ", double " mean );
.br
.BI "double QccMathLaplacianDensity(double " x ", double " variance ", double " mean );
.SH DESCRIPTION
.B QccMathMax()
returns the maximum of two numbers.  It is a macro defined as
.RS
.nf

#define QccMathMax(x, y) (((x) >= (y)) ? (x) : (y))
.fi
.RE
.LP
.B QccMathMin()
returns the minimum of two numbers.  It is a macro defined as
.RS
.nf

#define QccMathMax(x, y) (((x) <= (y)) ? (x) : (y))
.fi
.RE
.LP
.B QccMathPercent()
returns the percentage that
.I x
is of
.IR y .
It is a macro defined as
.RS
.nf

#define QccMathPercent(x, y) (((double)(x)/(y))*100.0)
.fi
.RE
.LP
.B QccMathModulus()
is a macro that calculates the signed remainder of
.I x
after division with
.IR y .
If 
.I y
is nonzero, 
.B QccMathModulus()
calculates
.RS
.nf

x - y * floor(x/y)

.fi
.RE
If
.I y
is zero, 
.B QccMathModulus()
simply evaluates to
.IR x .
.IR x
and
.IR y
can be integers or floating point.
.LP
.B QccMathLog2()
is a macro that calculates the logarithm base 2 of
.IR x .
.LP
.B QccMathMedian()
is a macro that calculates the median of the three values
.IR a ", " b ", and " c .
.LP
.B QccMathRand()
is a wrapper around
.BR random (3)
that ensures that
.BR random (3)
is properly seeded (by calling
.BR srandom (3)
with the current time)
the first time that
.B QccMathRand()
is called.
The return value of
.B QccMathRand()
is approximately uniformly distributed on the interval [0.0, 1.0].
.B Warning:
Although
.BR QccMathRand()
is MT-safe if the QccPack library is compiled with thread support
enabled, the underlying
.BR random (3)
and
.BR srandom (3)
functions are
.I not
MT-safe in typical systems. The implication is
that multithreaded application programs must not mix calls to 
.BR random (3)
and
.BR srandom (3)
with calls to
.BR QccMathRand() .
Use
.BR QccMathRand()
exclusively in 
.I all
threads.
.LP
.BR QccMathRandNormal()
returns a random number distributed according to a normal
density of mean 0 and unit variance.
The Box-Muller method is used to transform a pair of
uniformly distributed values (as generated by
.BR QccMathRand() )
into a normally distributed value.
.LP
.B QccMathGaussianDensity()
returns the value of the Gaussian (normal) density function
with the given
.I variance
and 
.IR mean .
It is equivalent to
.RS
.nf

return(exp((-(x - mean)*(x - mean))/2/variance)/sqrt(2*M_PI*variance));
.fi
.RE
.LP
.B QccMathLaplacianDensity()
returns the value of the Laplacian density function
with the given
.I variance
and 
.IR mean .
It is equivalent to
.RS
.nf

return(exp((-sqrt(2/variance))*fabs(x - mean))/sqrt(2*variance));
.fi
.RE
.SH "SEE ALSO"
.BR random (3),
.BR srandom (3),
.BR QccPack (3)
.SH AUTHOR
Copyright (C) 1997-2009  James E. Fowler
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