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Java Summary: Math and java.util.Random Classes Some basic math functions can be found in the Math class. The StrictMath class (not described here) may produce less accurate results and be slower, but will produce absolutely identical results, bit for bit, on all machines. Don't use StrictMath unless you need this very specific kind of portability. If you need numbers that exceed the range of long, use java.math.BigInteger. If you need to do exact decimal arithmetic, use java.math.BigDecimal, which gives complete control over precision and rounding, eg for financial calculations. Assume following declarations float f; double d, d1, d2; double ar; // angle in radians. x is any of int, long, float, or double. Math Constants Two common constants are defined in the Math class. double Math.E() Value of e, 2.718282..., base of the natural logarithms. double Math.PI() Value of pi, 3.14159265 .... Math Methods Trigonometric Methods All trigonometric method parameters are measured in radians, the normal mathematical system of angles, and not in degrees, the normal human angular measurement system. Use the toRadians or toDegrees methods to convert between these systems, or use the knowledge that there are 2*PI radians in 360 degrees. In addition to those below, the arc functions are also available. double Math.sin(ar) Returns the sine of ar. double Math.cos(ar) Returns the cosine of ar. double Math.tan(ar) Returns the tangent of ar. double Math.toRadians(d) Returns d (angle in degrees) converted to radians. double Math.toDegrees(ar) Returns ar (angle in radians) converted to degrees. Exponential Methods The two basic functions for logarithms and power are available. These both use the base e (Math.E) as is the usual case in mathematics. double Math.exp(d) Returns e (2.71...) to the power d. double Math.pow(d1, d2) Returns d1d2. double Math.log(d) Returns the logarithm of d to base e. Misc Methods double Math.sqrt(d) Returns the square root of d. t Math.abs(x) Returns absolute value of x with same type as the parameter: int, long, float, or double. t Math.max(x, y) Returns maximum of x and y with same type as the parameter: int, long, float, or double. t Math.min(x, y) Returns minimum of x and y with same type as the parameter: int, long, float, or double. Integer Related Methods The following methods translate floating point values to integer values, altho these values may still be stored in a double. double Math.floor(d) Returns the closest integer-valued double which is equal to or less than d. double Math.ceil(d) Returns the closest integer-valued double which is equal to or greater than d. double Math.rint(d) Returns the closest integer-valued double to d. long Math.round(d) Returns the long which is closest in value to the double d. int Math.round(f) Returns the int which is closest in value to the float f. Random Numbers For significantly more control over random number generation use the java.util.Random class (see below). double Math.random() Returns a number x in the range, 0.0 <= x < 1.0. java.util.Random Class The java.util.Random class provides more flexible ways to generate uniformly distributed random numbers, providing easy generation of types other than double, as well as providing a Gaussian distribution. Random Constructors It's necessary to construct a Random object. Random new Random(); Uses time in milliseconds as the seed. Random new Random(long seed); Uses the provided seed for testing purposes. Random Methods All methods return a uniform distribution of values, except nextGaussian(). Assume r is a Random object.. int r.nextInt(int n) Returns random int >= 0 and < n. int r.nextInt() Returns random int (full range). long r.nextLong() Returns random long (full range). float r.nextFloat() Returns random float >=0.0 and < 1.0. double r.nextDouble() Returns random double >=0.0 and < 1.0. boolean r.nextBoolean() Returns random boolean (true or false). double r.nextGaussian() Returns random double with mean 0.0 and standard deviation 1.0. Other math libraries I don't keep track of math libraries, but I'll add links below as I run across them. I have no idea if these are good or bad. jakarta.apache.org/commons/math/ - Apache Jakarta Math library. www.ia.hiof.no/~kyvh/SciLib/docs/scilib.html - SciLib Copyright 2005 Fred Swartz

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posted: | 8/17/2009 |

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