package chu_nz_baby;
import java.util.*;
import java.math.*;
/**
* <p>title:π 圆周率的计算 </p>
* <p>description:使用java bigdecimal完成圆周率(chudnovsky公式)的计算。可以指定计算精度和计算参数。 </p>
* <p>copyright: copyright (c) 2004</p>
* <a href="http://www.jason314.com/palgorithm.htm">圆周率的计算方法#chudnovsky公式</a>
* <a href="http://www.oursci.org/magazine/200301/030126.htm">圆周率π的计算历程</a>
* @author chu_nz_baby@hotmail.com
* @version 1.0
*/
public class pi {
private bigdecimal result;
public pi() {
}
public void run(int n, int scale) {
if(system.getproperty("debug") != null){
system.out.println("n=" + n);
}
bigdecimal upper = new bigdecimal(426880.0000 * math.sqrt(10005.0000));
upper = upper.setscale(scale, bigdecimal.round_half_even);
if(system.getproperty("debug") != null){
system.out.println("upper=" + upper);
}
bigdecimal downer = bigdecimal.valueof(0);
for (int i = 0; i <= n; i++) {
bigdecimal d0 = factorial(6 * i).multiply ( new bigdecimal( 545140134 * i + 13591409));
bigdecimal d1 = factorial(i);
bigdecimal d2 = pow(d1, 3);
bigdecimal d3 = factorial(3 * i);
bigdecimal d4 = pow(-640320, 3 * i);
bigdecimal d5 = d2.multiply(d3);
bigdecimal d6 = d4.multiply(d5);
bigdecimal d = d0.divide( d6, bigdecimal.round_half_even );
downer = downer.add(d);
}
if(system.getproperty("debug") != null){
system.out.println("downer=" + downer);
}
if(system.getproperty("debug") != null){
system.out.println("upper.scale = " + upper.scale());
system.out.println("downer.scale = " + downer.scale());
}
result = upper.divide(downer, bigdecimal.round_half_even);
if(system.getproperty("debug") != null){
system.out.println("result.scale = " + result.scale());
}
}
public bigdecimal getresult() {
return result;
}
public static bigdecimal pow(double val, int power){
return pow(new bigdecimal(val), power);
}
public static bigdecimal pow(bigdecimal val, int power){
bigdecimal value = bigdecimal.valueof(1);
for(int i = 1; i <= power; i ++){
value = value.multiply(val);
}
return value;
}
public static bigdecimal factorial(int n){
bigdecimal value = bigdecimal.valueof(1);
for(int i = 1; i <=n ; i++){
value = value.multiply(bigdecimal.valueof(i));
}
return value;
}
public static void main(string[] args) {
if(args.length < 2){
system.out.println("usage: " + "java nz-baby.pi " + " 参数(0-无穷大) 精度(1-4294967296)");
system.out.println("usage: " + "java nz-baby.pi " + " n(0- ) scale(1-4294967296)");
system.exit(-1);
}
int n = integer.parseint(args[0]);
int scale = integer.parseint(args[1]);
system.out.println("palgorithm n=" + n + " scale=" + scale);
system.out.println("start:" + new date(system.currenttimemillis()));
pi p = new pi();
p.run(n, scale);
system.out.println("end:" + new date(system.currenttimemillis()));
system.out.println("result=" + p.getresult());
}
}
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