org.lcsim.recon.tracking.trfutil

Class TRFMath

java.lang.Object

org.lcsim.recon.tracking.trfutil.TRFMath

public final class TRFMath
extends Object

The component TRFMath includes some mathematical constants (PI, TWOPI and PI2), some physical constants (CLIGHT and BFAC) and some utility functions. These include two modulus-related functions, fmod1 and fmod2, and asin(x)/x . There are also functions is_equal and is_zero which provide for the comparison of two floating point values allowing for some numerical roundoff. Modelled on the C++ class, so contains some superfluous functionality which is preserved to maintain a similarity to the C++ code.

Version:

1.0

Author:

Norman A. Graf

Field Summary

Fields

Modifier and Type	Field and Description
static double	BFAC Factor connecting curvature to momentum.
static double	CLIGHT Speed of light.
static double	PI2 PI/2
static double	TWOPI 2*PI

Constructor Summary

Constructors

Modifier	Constructor and Description
private	TRFMath()

Method Summary

Methods

Modifier and Type	Method and Description
static double	asinrat(double x) asinrat = asin(x)/x
static double	fmod1(double value, double range) Similar to fmod but returns value in positive range only.
static double	fmod2(double value, double range) Similar to fmod1 but returns range (-R/2,R/2) instead of (0,R).
static boolean	isEqual(double x1, double x2) Function is_equal returns true if values are exactly the same or differ by a very small amount.
static boolean	isZero(double x) Function is_zero returns true if the value is within epsilon of zero.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

TWOPI

public static double TWOPI

2*PI

PI2

public static double PI2

PI/2

CLIGHT

public static double CLIGHT

Speed of light. 2.99792458e10 cm/sec.

BFAC

public static double BFAC

Factor connecting curvature to momentum. C = 1/Rc = BFAC * B * q/pT where B = magnetic field in Tesla, q = charge in natural units (electron has -1) and pT = transverse momentum in GeV/c Numerical value is 1.0e-13 * CLIGHT .

Constructor Detail

TRFMath

private TRFMath()

Method Detail

fmod1

public static double fmod1(double value,
           double range)

Similar to fmod but returns value in positive range only.

Parameters:

value - double value to convert.

range - double range for modulus.

Returns:

double value in range (0,range).

fmod2

public static double fmod2(double value,
           double range)

Similar to fmod1 but returns range (-R/2,R/2) instead of (0,R).

Parameters:

value - double value to convert.

range - double half-range for modulus.

Returns:

double value in range (-range/2,range/2).

asinrat

public static double asinrat(double x)

asinrat = asin(x)/x

Parameters:

x - value for which to calculate asin(x)/x

Returns:

arcsin(x)/x using series expansion for small x.

isZero

public static boolean isZero(double x)

Function is_zero returns true if the value is within epsilon of zero. By definition, 1.0+epsilon is the closest value to 1.0. Thus, this function is sensible for variables whose natural scale or range is 1.0.

Parameters:

x - value to check against zero

Returns:

approximation to zero accounting for roundoff.

isEqual

public static boolean isEqual(double x1,
              double x2)

Function is_equal returns true if values are exactly the same or differ by a very small amount. We set that small amount to be twice the machine precision. Values differing by one tick will return true, those differing by three or more will return false. The behavior for those differing by two depends on the value and the platform.

Parameters:

x1 - value 1

x2 - value 2

Returns:

true if equal or equals within precision.