com.numericalmethod.suanshu.number
Class NumberUtils

java.lang.Object
  com.numericalmethod.suanshu.number.NumberUtils

public class NumberUtils
extends java.lang.Object

This class collects the utility functions to manipulate data of type Number.

These functions are static and stateless.

Nested Class Summary

static interface

NumberUtils.Comparable<T extends java.lang.Number> We need a precision parameter to determine whether two numbers are close enough to be treated as equal.

Method Summary

static int	compare(java.lang.Number num1, java.lang.Number num2, double epsilon) Compare two Numbers.
static boolean	equal(java.lang.Number num1, java.lang.Number num2, double epsilon) Check the equality of two Numbers, up to a precision.
static boolean	isReal(java.lang.Number number) Check if a Number is a real number.
static java.lang.Number	parse(java.lang.String str) Construct a Number from a String.

Methods inherited from class java.lang.Object

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

Method Detail

equal

public static boolean equal(java.lang.Number num1,
                            java.lang.Number num2,
                            double epsilon)

Check the equality of two Numbers, up to a precision.

This method compares two numbers up to a precision. The input type must subclass Number and implements NumberUtils.Comparable.

Parameters:

num1 - a number

num2 - a number

epsilon - a precision parameter: when a number |x| ≤ ε, it is considered 0

Returns:

true if their double values are equal as defined by DoubleUtils.equal(double, double, double), or by the Object's Object.equals(java.lang.Object); false otherwise

compare

public static int compare(java.lang.Number num1,
                          java.lang.Number num2,
                          double epsilon)

Compare two Numbers.

The two inputs can be different subclasses of Number.

• If both can be casted to double, they are compared in the double domain; e.g., 2 vs. new Double(3)
• If one is a double, then it is casted into the same Field as the other number for comparison; e.g., 4 vs. 3 + 0i
• If neither is double, then the two numbers must be of the same class for comparison; e.g., Complex.

Parameters:

num1 - a Number

num2 - a Number

epsilon - a precision parameter: when a number |x| ≤ ε, it is considered 0; e.g., 1e-9

Returns:

0 if d1 is close enough to d2, 1 if d1 > d2, -1 if d1 < d2

isReal

public static boolean isReal(java.lang.Number number)

Check if a Number is a real number. Specifically, we check whether doubleValue() can be called meaningfully.

TODO: this function needs to be extended or modified when a new Number subclass is implemented.

Parameters:

number - a number

Returns:

true iff the number is real, i.e., in Rⁿ

parse

public static java.lang.Number parse(java.lang.String str)

Construct a Number from a String.

E.g.,

 "2"
 "2."
 "3 + 5i"
 "1.23 - 4.56i"
 "-1.23 - 4.56i"
 "-1.23 - 4.56e-7i"
 "-1.23 - 4.56+e7i"
 "i"
 

Note: having spaces in the real part between sign and number is illegal, e.g.,

 - 1.23+4.56i
 + 1.23+4.56i
 

Parameters:

str - a number in String format

Returns:

a number of type subclass Number such as Double, Complex