FloatFunctions (Parallel Colt 0.10.1-SNAPSHOT

java.lang.Object
- cern.jet.math.tfloat.FloatFunctions

public class FloatFunctions
extends Object

Function objects to be passed to generic methods. Contains the functions of Math as function objects, as well as a few more basic functions.

Function objects conveniently allow to express arbitrary functions in a generic manner. Essentially, a function object is an object that can perform a function on some arguments. It has a minimal interface: a method apply that takes the arguments, computes something and returns some result value. Function objects are comparable to function pointers in C used for call-backs.

Unary functions are of type FloatFunction , binary functions of type FloatFloatFunction . All can be retrieved via public static final variables named after the function. Unary predicates are of type FloatProcedure, binary predicates of type FloatFloatProcedure. All can be retrieved via public static final variables named isXXX.

Binary functions and predicates also exist as unary functions with the second argument being fixed to a constant. These are generated and retrieved via factory methods (again with the same name as the function). Example:

Functions.pow gives the function a^b.
Functions.pow.apply(2,3)==8.
Functions.pow(3) gives the function a³.
Functions.pow(3).apply(2)==8.

More general, any binary function can be made an unary functions by fixing either the first or the second argument. See methods bindArg1(FloatFloatFunction,float) and bindArg2(FloatFloatFunction,float). The order of arguments can be swapped so that the first argument becomes the second and vice-versa. See method swapArgs(FloatFloatFunction). Example:

Functions.pow gives the function a^b.
Functions.bindArg2(Functions.pow,3) gives the function x³.
Functions.bindArg1(Functions.pow,3) gives the function 3^x.
Functions.swapArgs(Functions.pow) gives the function b^a.

Even more general, functions can be chained (composed, assembled). Assume we have two unary functions g and h. The unary function g(h(a)) applying both in sequence can be generated via chain(FloatFunction,FloatFunction):

Functions.chain(g,h);

Assume further we have a binary function f. The binary function g(f(a,b)) can be generated via chain(FloatFunction,FloatFloatFunction):

Functions.chain(g,f);

The binary function f(g(a),h(b)) can be generated via chain(FloatFloatFunction,FloatFunction,FloatFunction):

Functions.chain(f,g,h);

Arbitrarily complex functions can be composed from these building blocks. For example sin(a) + cos²(b) can be specified as follows:

chain(plus,sin,chain(square,cos));

or, of course, as

 new FloatFloatFunction() {
     public final float apply(float a, float b) {
         return Math.sin(a) + Math.pow(Math.cos(b), 2);
     }
 }

For aliasing see functions. Try this

 // should yield 1.4399560356056456 in all cases
 float a = 0.5;
 float b = 0.2;
 float v = Math.sin(a) + Math.pow(Math.cos(b), 2);
 System.out.println(v);
 Functions F = Functions.functions;
 FloatFloatFunction f = F.chain(F.plus, F.sin, F.chain(F.square, F.cos));
 System.out.println(f.apply(a, b));
 FloatFloatFunction g = new FloatFloatFunction() {
     public float apply(float a, float b) {
         return Math.sin(a) + Math.pow(Math.cos(b), 2);
     }
 };
 System.out.println(g.apply(a, b));

Performance

Surprise. Using modern non-adaptive JITs such as SunJDK 1.2.2 (java -classic) there seems to be no or only moderate performance penalty in using function objects in a loop over traditional code in a loop. For complex nested function objects (e.g. F.chain(F.abs,F.chain(F.plus,F.sin,F.chain(F.square,F.cos)))) the penalty is zero, for trivial functions (e.g. F.plus) the penalty is often acceptable.

Iteration Performance [million function evaluations per second] Pentium Pro 200 Mhz, SunJDK 1.2.2, NT, java -classic,
	30000000 iterations	3000000 iterations (10 times less)
	`F.plus`	`a+b`	`F.chain(F.abs,F.chain(F.plus,F.sin,F.chain(F.square,F.cos)))`	`Math.abs(Math.sin(a) + Math.pow(Math.cos(b),2))`
	10.8	29.6	0.43	0.35

Version:: 1.0, 09/24/99
Author:: wolfgang.hoschek@cern.ch

Field Summary

Fields
Modifier and Type	Field and Description
`static FloatFunction`	`abs` Function that returns `Math.abs(a)`.
`static FloatFunction`	`acos` Function that returns `Math.acos(a)`.
`static FloatFunction`	`asin` Function that returns `Math.asin(a)`.
`static FloatFunction`	`atan` Function that returns `Math.atan(a)`.
`static FloatFloatFunction`	`atan2` Function that returns `Math.atan2(a,b)`.
`static FloatFunction`	`ceil` Function that returns `Math.ceil(a)`.
`static FloatFloatFunction`	`compare` Function that returns `a < b ? -1 : a > b ? 1 : 0`.
`static FloatFunction`	`cos` Function that returns `Math.cos(a)`.
`static FloatFloatFunction`	`div` Function that returns `a / b`.
`static FloatFloatFunction`	`divNeg` Function that returns `-(a / b)`.
`static FloatFloatFunction`	`equals` Function that returns `a == b ? 1 : 0`.
`static FloatFunction`	`exp` Function that returns `Math.exp(a)`.
`static FloatFunction`	`floor` Function that returns `Math.floor(a)`.
`static FloatFunctions`	`functions` Little trick to allow for "aliasing", that is, renaming this class.
`static FloatFloatFunction`	`greater` Function that returns `a > b ? 1 : 0`.
`static FloatFunction`	`identity` Function that returns its argument.
`static FloatFloatFunction`	`IEEEremainder` Function that returns `Math.IEEEremainder(a,b)`.
`static FloatFunction`	`inv` Function that returns `1.0 / a`.
`static FloatFloatProcedure`	`isEqual` Function that returns `a == b`.
`static FloatFloatProcedure`	`isGreater` Function that returns `a > b`.
`static FloatFloatProcedure`	`isLess` Function that returns `a < b`.
`static FloatFloatFunction`	`less` Function that returns `a < b ? 1 : 0`.
`static FloatFloatFunction`	`lg` Function that returns `Math.log(a) / Math.log(b)`.
`static FloatFunction`	`log` Function that returns `Math.log(a)`.
`static FloatFunction`	`log2` Function that returns `Math.log(a) / Math.log(2)`.
`static FloatFloatFunction`	`max` Function that returns `Math.max(a,b)`.
`static FloatFloatFunction`	`min` Function that returns `Math.min(a,b)`.
`static FloatFloatFunction`	`minus` Function that returns `a - b`.
`static FloatFloatFunction`	`mod` Function that returns `a % b`.
`static FloatFloatFunction`	`mult` Function that returns `a * b`.
`static FloatFloatFunction`	`multNeg` Function that returns `-(a * b)`.
`static FloatFloatFunction`	`multSquare` Function that returns `a * b^2`.
`static FloatFunction`	`neg` Function that returns `-a`.
`static FloatFloatFunction`	`plus` Function that returns `a + b`.
`static FloatFloatFunction`	`plusAbs` Function that returns `Math.abs(a) + Math.abs(b)`.
`static FloatFloatFunction`	`pow` Function that returns `Math.pow(a,b)`.
`static FloatFunction`	`rint` Function that returns `Math.rint(a)`.
`static FloatFunction`	`sign` Function that returns `a < 0 ? -1 : a > 0 ? 1 : 0`.
`static FloatFunction`	`sin` Function that returns `Math.sin(a)`.
`static FloatFunction`	`sqrt` Function that returns `Math.sqrt(a)`.
`static FloatFunction`	`square` Function that returns `a * a`.
`static FloatFunction`	`tan` Function that returns `Math.tan(a)`.

Method Summary

Methods
Modifier and Type	Method and Description
`static FloatFunction`	`between(float from, float to)` Constructs a function that returns `(from<=a && a<=to) ? 1 : 0`.
`static FloatFunction`	`bindArg1(FloatFloatFunction function, float c)` Constructs a unary function from a binary function with the first operand (argument) fixed to the given constant `c`.
`static FloatFunction`	`bindArg2(FloatFloatFunction function, float c)` Constructs a unary function from a binary function with the second operand (argument) fixed to the given constant `c`.
`static FloatFloatFunction`	`chain(FloatFloatFunction f, FloatFunction g, FloatFunction h)` Constructs the function `f( g(a), h(b) )`.
`static FloatFloatFunction`	`chain(FloatFunction g, FloatFloatFunction h)` Constructs the function `g( h(a,b) )`.
`static FloatFunction`	`chain(FloatFunction g, FloatFunction h)` Constructs the function `g( h(a) )`.
`static FloatFunction`	`compare(float b)` Constructs a function that returns `a < b ? -1 : a > b ? 1 : 0`.
`static FloatFunction`	`constant(float c)` Constructs a function that returns the constant `c`.
`static void`	`demo1()` Demonstrates usage of this class.
`static void`	`demo2(int size)` Benchmarks and demonstrates usage of trivial and complex functions.
`static FloatFunction`	`div(float b)` Constructs a function that returns `a / b`.
`static FloatFunction`	`equals(float b)` Constructs a function that returns `a == b ? 1 : 0`.
`static FloatFunction`	`greater(float b)` Constructs a function that returns `a > b ? 1 : 0`.
`static FloatFunction`	`IEEEremainder(float b)` Constructs a function that returns `Math.IEEEremainder(a,b)`.
`static FloatProcedure`	`isBetween(float from, float to)` Constructs a function that returns `from<=a && a<=to`.
`static FloatProcedure`	`isEqual(float b)` Constructs a function that returns `a == b`.
`static FloatProcedure`	`isGreater(float b)` Constructs a function that returns `a > b`.
`static FloatProcedure`	`isLess(float b)` Constructs a function that returns `a < b`.
`static FloatFunction`	`less(float b)` Constructs a function that returns `a < b ? 1 : 0`.
`static FloatFunction`	`lg(float b)` Constructs a function that returns `Math.log(a) / Math.log(b)`.
`static FloatFunction`	`max(float b)` Constructs a function that returns `Math.max(a,b)`.
`static FloatFunction`	`min(float b)` Constructs a function that returns `Math.min(a,b)`.
`static FloatFunction`	`minus(float b)` Constructs a function that returns `a - b`.
`static FloatFloatFunction`	`minusMult(float constant)` Constructs a function that returns `a - b*constant`.
`static FloatFunction`	`mod(float b)` Constructs a function that returns `a % b`.
`static FloatFunction`	`mult(float b)` Constructs a function that returns `a * b`.
`static FloatFloatFunction`	`multSecond(float constant)`
`static FloatFunction`	`plus(float b)` Constructs a function that returns `a + b`.
`static FloatFloatFunction`	`plusMultFirst(float constant)` Constructs a function that returns `a * constant + b`.
`static FloatFloatFunction`	`plusMultSecond(float constant)` Constructs a function that returns `a + b*constant`.
`static FloatFunction`	`pow(float b)` Constructs a function that returns `Math.pow(a,b)`.
`static FloatFunction`	`random()` Constructs a function that returns a new uniform random number in the open unit interval `(0.0,1.0)` (excluding 0.0 and 1.0).
`static FloatFunction`	`round(float precision)` Constructs a function that returns the number rounded to the given precision; `Math.rint(a/precision)*precision`.
`static FloatFloatFunction`	`swapArgs(FloatFloatFunction function)` Constructs a function that returns `function.apply(b,a)`, i.e.

Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - functions
```
public static final FloatFunctions functions
```
    Little trick to allow for "aliasing", that is, renaming this class. Writing code like
    Functions.chain(Functions.plus,Functions.sin,Functions.chain(Functions.square,Functions.cos));
    is a bit awkward, to say the least. Using the aliasing you can instead write
    Functions F = Functions.functions; F.chain(F.plus,F.sin,F.chain(F.square,F.cos));
  - abs
```
public static final FloatFunction abs
```
    Function that returns Math.abs(a).
  - acos
```
public static final FloatFunction acos
```
    Function that returns Math.acos(a).
  - asin
```
public static final FloatFunction asin
```
    Function that returns Math.asin(a).
  - atan
```
public static final FloatFunction atan
```
    Function that returns Math.atan(a).
  - ceil
```
public static final FloatFunction ceil
```
    Function that returns Math.ceil(a).
  - cos
```
public static final FloatFunction cos
```
    Function that returns Math.cos(a).
  - exp
```
public static final FloatFunction exp
```
    Function that returns Math.exp(a).
  - floor
```
public static final FloatFunction floor
```
    Function that returns Math.floor(a).
  - identity
```
public static final FloatFunction identity
```
    Function that returns its argument.
  - inv
```
public static final FloatFunction inv
```
    Function that returns 1.0 / a.
  - log
```
public static final FloatFunction log
```
    Function that returns Math.log(a).
  - log2
```
public static final FloatFunction log2
```
    Function that returns Math.log(a) / Math.log(2).
  - neg
```
public static final FloatFunction neg
```
    Function that returns -a.
  - rint
```
public static final FloatFunction rint
```
    Function that returns Math.rint(a).
  - sign
```
public static final FloatFunction sign
```
    Function that returns a < 0 ? -1 : a > 0 ? 1 : 0.
  - sin
```
public static final FloatFunction sin
```
    Function that returns Math.sin(a).
  - sqrt
```
public static final FloatFunction sqrt
```
    Function that returns Math.sqrt(a).
  - square
```
public static final FloatFunction square
```
    Function that returns a * a.
  - tan
```
public static final FloatFunction tan
```
    Function that returns Math.tan(a).
  - atan2
```
public static final FloatFloatFunction atan2
```
    Function that returns Math.atan2(a,b).
  - compare
```
public static final FloatFloatFunction compare
```
    Function that returns a < b ? -1 : a > b ? 1 : 0.
  - div
```
public static final FloatFloatFunction div
```
    Function that returns a / b.
  - divNeg
```
public static final FloatFloatFunction divNeg
```
    Function that returns -(a / b).
  - equals
```
public static final FloatFloatFunction equals
```
    Function that returns a == b ? 1 : 0.
  - greater
```
public static final FloatFloatFunction greater
```
    Function that returns a > b ? 1 : 0.
  - IEEEremainder
```
public static final FloatFloatFunction IEEEremainder
```
    Function that returns Math.IEEEremainder(a,b).
  - isEqual
```
public static final FloatFloatProcedure isEqual
```
    Function that returns a == b.
  - isLess
```
public static final FloatFloatProcedure isLess
```
    Function that returns a < b.
  - isGreater
```
public static final FloatFloatProcedure isGreater
```
    Function that returns a > b.
  - less
```
public static final FloatFloatFunction less
```
    Function that returns a < b ? 1 : 0.
  - lg
```
public static final FloatFloatFunction lg
```
    Function that returns Math.log(a) / Math.log(b).
  - max
```
public static final FloatFloatFunction max
```
    Function that returns Math.max(a,b).
  - min
```
public static final FloatFloatFunction min
```
    Function that returns Math.min(a,b).
  - minus
```
public static final FloatFloatFunction minus
```
    Function that returns a - b.
  - mod
```
public static final FloatFloatFunction mod
```
    Function that returns a % b.
  - mult
```
public static final FloatFloatFunction mult
```
    Function that returns a * b.
  - multNeg
```
public static final FloatFloatFunction multNeg
```
    Function that returns -(a * b).
  - multSquare
```
public static final FloatFloatFunction multSquare
```
    Function that returns a * b^2.
  - plus
```
public static final FloatFloatFunction plus
```
    Function that returns a + b.
  - plusAbs
```
public static final FloatFloatFunction plusAbs
```
    Function that returns Math.abs(a) + Math.abs(b).
  - pow
```
public static final FloatFloatFunction pow
```
    Function that returns Math.pow(a,b).
- Method Detail
  - between
```
public static FloatFunction between(float from,
                    float to)
```
    Constructs a function that returns (from<=a && a<=to) ? 1 : 0. a is a variable, from and to are fixed.
  - bindArg1
```
public static FloatFunction bindArg1(FloatFloatFunction function,
                     float c)
```
    Constructs a unary function from a binary function with the first operand (argument) fixed to the given constant c. The second operand is variable (free).
    
    Parameters:
    function - a binary function taking operands in the form function.apply(c,var).
    
    Returns:
    the unary function function(c,var).
  - bindArg2
```
public static FloatFunction bindArg2(FloatFloatFunction function,
                     float c)
```
    Constructs a unary function from a binary function with the second operand (argument) fixed to the given constant c. The first operand is variable (free).
    
    Parameters:
    function - a binary function taking operands in the form function.apply(var,c).
    
    Returns:
    the unary function function(var,c).
  - chain
```
public static FloatFloatFunction chain(FloatFloatFunction f,
                       FloatFunction g,
                       FloatFunction h)
```
    Constructs the function f( g(a), h(b) ).
    
    Parameters:
    f - a binary function.
    g - a unary function.
    h - a unary function.
    
    Returns:
    the binary function f( g(a), h(b) ).
  - chain
```
public static FloatFloatFunction chain(FloatFunction g,
                       FloatFloatFunction h)
```
    Constructs the function g( h(a,b) ).
    
    Parameters:
    g - a unary function.
    h - a binary function.
    
    Returns:
    the unary function g( h(a,b) ).
  - chain
```
public static FloatFunction chain(FloatFunction g,
                  FloatFunction h)
```
    Constructs the function g( h(a) ).
    
    Parameters:
    g - a unary function.
    h - a unary function.
    
    Returns:
    the unary function g( h(a) ).
  - compare
```
public static FloatFunction compare(float b)
```
    Constructs a function that returns a < b ? -1 : a > b ? 1 : 0. a is a variable, b is fixed.
  - constant
```
public static FloatFunction constant(float c)
```
    Constructs a function that returns the constant c.
  - demo1
```
public static void demo1()
```
    Demonstrates usage of this class.
  - demo2
```
public static void demo2(int size)
```
    Benchmarks and demonstrates usage of trivial and complex functions.
  - div
```
public static FloatFunction div(float b)
```
    Constructs a function that returns a / b. a is a variable, b is fixed.
  - equals
```
public static FloatFunction equals(float b)
```
    Constructs a function that returns a == b ? 1 : 0. a is a variable, b is fixed.
  - greater
```
public static FloatFunction greater(float b)
```
    Constructs a function that returns a > b ? 1 : 0. a is a variable, b is fixed.
  - IEEEremainder
```
public static FloatFunction IEEEremainder(float b)
```
    Constructs a function that returns Math.IEEEremainder(a,b). a is a variable, b is fixed.
  - isBetween
```
public static FloatProcedure isBetween(float from,
                       float to)
```
    Constructs a function that returns from<=a && a<=to. a is a variable, from and to are fixed.
  - isEqual
```
public static FloatProcedure isEqual(float b)
```
    Constructs a function that returns a == b. a is a variable, b is fixed.
  - isGreater
```
public static FloatProcedure isGreater(float b)
```
    Constructs a function that returns a > b. a is a variable, b is fixed.
  - isLess
```
public static FloatProcedure isLess(float b)
```
    Constructs a function that returns a < b. a is a variable, b is fixed.
  - less
```
public static FloatFunction less(float b)
```
    Constructs a function that returns a < b ? 1 : 0. a is a variable, b is fixed.
  - lg
```
public static FloatFunction lg(float b)
```
    Constructs a function that returns Math.log(a) / Math.log(b). a is a variable, b is fixed.
  - max
```
public static FloatFunction max(float b)
```
    Constructs a function that returns Math.max(a,b). a is a variable, b is fixed.
  - min
```
public static FloatFunction min(float b)
```
    Constructs a function that returns Math.min(a,b). a is a variable, b is fixed.
  - minus
```
public static FloatFunction minus(float b)
```
    Constructs a function that returns a - b. a is a variable, b is fixed.
  - minusMult
```
public static FloatFloatFunction minusMult(float constant)
```
    Constructs a function that returns a - b*constant. a and b are variables, constant is fixed.
  - mod
```
public static FloatFunction mod(float b)
```
    Constructs a function that returns a % b. a is a variable, b is fixed.
  - mult
```
public static FloatFunction mult(float b)
```
    Constructs a function that returns a * b. a is a variable, b is fixed.
  - plus
```
public static FloatFunction plus(float b)
```
    Constructs a function that returns a + b. a is a variable, b is fixed.
  - multSecond
```
public static FloatFloatFunction multSecond(float constant)
```
  - plusMultSecond
```
public static FloatFloatFunction plusMultSecond(float constant)
```
    Constructs a function that returns a + b*constant. a and b are variables, constant is fixed.
  - plusMultFirst
```
public static FloatFloatFunction plusMultFirst(float constant)
```
    Constructs a function that returns a * constant + b. a and b are variables, constant is fixed.
  - pow
```
public static FloatFunction pow(float b)
```
    Constructs a function that returns Math.pow(a,b). a is a variable, b is fixed.
  - random
```
public static FloatFunction random()
```
    Constructs a function that returns a new uniform random number in the open unit interval (0.0,1.0) (excluding 0.0 and 1.0). Currently the engine is FloatMersenneTwister and is seeded with the current time.
    Note that any random engine derived from FloatRandomEngine and any random distribution derived from AbstractFloatDistribution are function objects, because they implement the proper interfaces. Thus, if you are not happy with the default, just pass your favourite random generator to function evaluating methods.
  - round
```
public static FloatFunction round(float precision)
```
    Constructs a function that returns the number rounded to the given precision; Math.rint(a/precision)*precision. Examples:
```
 precision = 0.01 rounds 0.012 --> 0.01, 0.018 --> 0.02
 precision = 10   rounds 123   --> 120 , 127   --> 130
 
```
  - swapArgs
```
public static FloatFloatFunction swapArgs(FloatFloatFunction function)
```
    Constructs a function that returns function.apply(b,a), i.e. applies the function with the first operand as second operand and the second operand as first operand.
    
    Parameters:
    function - a function taking operands in the form function.apply(a,b).
    
    Returns:
    the binary function function(b,a).

Class FloatFunctions

Performance

Field Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

functions

abs

acos

asin

atan

ceil

cos

exp

floor

identity

inv

log

log2

neg

rint

sign

sin

sqrt

square

tan

atan2

compare

div

divNeg

equals

greater

IEEEremainder

isEqual

isLess

isGreater

less

lg

max

min

minus

mod

mult

multNeg

multSquare

plus

plusAbs

pow

Method Detail

between

bindArg1

bindArg2

chain

chain

chain

compare

constant

demo1

demo2

div

equals

greater

IEEEremainder

isBetween

isEqual

isGreater

isLess

less

lg

max

min

minus

minusMult

mod

mult

plus

multSecond

plusMultSecond

plusMultFirst

pow