[英]Why is this division with BigDecimal returning 0?
I am using the Chudnovsky algorithm to compute PI: 我正在使用Chudnovsky算法来计算PI:
Here is the code: 这是代码:
import java.math.BigDecimal;
import java.math.MathContext;
import java.util.Scanner;
public class main {
public static void main(String[] args) {
Scanner reader = new Scanner(System.in);
int summationUpperLimit;
int precision;
System.out.println("Enter the summation upper limit: ");
summationUpperLimit = reader.nextInt();
System.out.println("Enter the precision: ");
precision = reader.nextInt();
System.out.println(calculatePI(summationUpperLimit, precision));
}
private static int calculateFactorial(int n) {
int factorial = 1;
for (; n > 1; n--) {
factorial = factorial * n;
}
return factorial;
}
private static BigDecimal calculatePI(int summationUpperLimit, int precision) {
BigDecimal reciprocalOfPI = BigDecimal.ZERO;
reciprocalOfPI.setScale(precision - 1, BigDecimal.ROUND_HALF_UP);
for (int k = 0; k <= summationUpperLimit; k++) {
BigDecimal numerator = BigDecimal.valueOf(12 * Math.pow(-1, k) * calculateFactorial(6 * k) * (13591409 + 545140134 * k));
numerator.setScale(precision - 1, BigDecimal.ROUND_HALF_UP);
BigDecimal denominator = BigDecimal.valueOf(calculateFactorial(3 * k) + Math.pow(calculateFactorial(k), 3) * Math.pow(640320, 3 * k + 1.5));
denominator.setScale(precision - 1, BigDecimal.ROUND_HALF_UP);
// The issue is the line below:
reciprocalOfPI = reciprocalOfPI.add(numerator.divide(denominator, BigDecimal.ROUND_HALF_UP));
}
return reciprocalOfPI.pow(-1, MathContext.DECIMAL128);
}
}
I set the following input: 我设置以下输入:
summationUpperLimit = 0
precision = 100
In debugging mode, I checked the output: 在调试模式下,我检查了输出:
numerator = 163096908
denominator = 512384048.99600077
reciprocalOfPI = 0 (this value was taken after the division)
163096908 / 512384048.99600077 doesn't equal 0 so why is the expression reciprocalOfPI = reciprocalOfPI.add(numerator.divide(denominator, BigDecimal.ROUND_HALF_UP));
163096908 / 512384048.99600077不等于0,为什么表达式
reciprocalOfPI = reciprocalOfPI.add(numerator.divide(denominator, BigDecimal.ROUND_HALF_UP));
setting reciprocalOfPI
to 0? 将
reciprocalOfPI
设置为0?
My justification for setting scale = precision - 1
: 我的理由是设置
scale = precision - 1
:
Precision is the total number of digits. 精度是数字的总数。 Scale is the number of digits after the decimal place.
小数位数是小数点后的位数。
In PI, there is only 1 digit before the decimal. 在PI中,小数点前只有1位数字。
precision = scale + 1
and therefore scale = precision - 1
precision = scale + 1
,因此scale = precision - 1
It's probably caused by 这可能是由于
reciprocalOfPI.setScale(precision - 1, BigDecimal.ROUND_HALF_UP);
which should be 应该是
reciprocalOfPI = reciprocalOfPI.setScale(precision - 1, BigDecimal.ROUND_HALF_UP);
BigDecimal is immutable. BigDecimal是不可变的。 All its "mutating" methods return a new BigDecimal, leaving the original one unchanged.
它的所有“变异”方法都返回一个新的BigDecimal,而原始的则保持不变。
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