Almkvist-Giullera formula for pi: Difference between revisions
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pi to 70 decimals: 3.1415926535897932384626433832795028841971693993751058209749445923078164
</pre>
=={{header|Java}}==
<syntaxhighlight lang="java">
import java.math.BigDecimal;
import java.math.BigInteger;
import java.math.MathContext;
import java.math.RoundingMode;
public final class AlmkvistGiulleraFormula {
public static void main(String[] aArgs) {
System.out.println("n Integer part");
System.out.println("================================================");
for ( int n = 0; n <= 9; n++ ) {
System.out.println(String.format("%d%47s", n, almkvistGiullera(n).toString()));
}
final MathContext mathContext = new MathContext(71, RoundingMode.HALF_EVEN);
final BigDecimal epsilon = BigDecimal.ONE.divide(BigDecimal.TEN.pow(70));
BigDecimal previous = BigDecimal.ONE;
BigDecimal sum = BigDecimal.ZERO;
BigDecimal pi = BigDecimal.ZERO;
int n = 0;
while ( pi.subtract(previous).abs().compareTo(epsilon) >= 0 ) {
BigDecimal nextTerm = new BigDecimal(almkvistGiullera(n)).divide(BigDecimal.TEN.pow(6 * n + 3));
sum = sum.add(nextTerm);
previous = pi;
n += 1;
pi = BigDecimal.ONE.divide(sum, mathContext).sqrt(mathContext);
}
System.out.println(System.lineSeparator() + "pi to 70 decimal places:");
System.out.println(pi);
}
// The integer part of the n'th term of Almkvist-Giullera series.
private static BigInteger almkvistGiullera(int aN) {
BigInteger term1 = factorial(6 * aN).multiply(BigInteger.valueOf(32));
BigInteger term2 = BigInteger.valueOf(532 * aN * aN + 126 * aN + 9);
BigInteger term3 = factorial(aN).pow(6).multiply(BigInteger.valueOf(3));
return term1.multiply(term2).divide(term3);
}
private static BigInteger factorial(int aNumber) {
BigInteger result = BigInteger.ONE;
for ( int i = 2; i <= aNumber; i++ ) {
result = result.multiply(BigInteger.valueOf(i));
}
return result;
}
}
</syntaxhighlight>
{{ out }}
<pre>
n Integer part
================================================
0 96
1 5122560
2 190722470400
3 7574824857600000
4 312546150372456000000
5 13207874703225491420651520
6 567273919793089083292259942400
7 24650600248172987140112763715584000
8 1080657854354639453670407474439566400000
9 47701779391594966287470570490839978880000000
pi to 70 decimal places:
3.1415926535897932384626433832795028841971693993751058209749445923078164
</pre>
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