Pell's equation
From Rosetta Code
You are encouraged to solve this task according to the task description, using any language you may know.
Pell's equation is a Diophantine equation of the form
- x2 - ny2 = 1
with integer solutions for x and y, where n is a given nonsquare positive integer.
- Task requirements
-
- find the smallest solution in positive integers to Pell's equation for n = {61, 109, 181, 277}.
- See also
-
- Wikipedia entry: Pell's equation.
C#[edit]
using System;
using System.Numerics;
static class Program
{
static void Fun(ref BigInteger a, ref BigInteger b, int c)
{
BigInteger t = a; a = b; b = b * c + t;
}
static void SolvePell(int n, ref BigInteger a, ref BigInteger b)
{
int x = (int)Math.Sqrt(n), y = x, z = 1, r = x << 1;
BigInteger e1 = 1, e2 = 0, f1 = 0, f2 = 1;
while (true)
{
y = r * z - y; z = (n - y * y) / z; r = (x + y) / z;
Fun(ref e1, ref e2, r); Fun(ref f1, ref f2, r); a = f2; b = e2; Fun(ref b, ref a, x);
if (a * a - n * b * b == 1) return;
}
}
static void Main()
{
BigInteger x, y; foreach (int n in new[] { 61, 109, 181, 277 })
{
SolvePell(n, ref x, ref y);
Console.WriteLine("x^2 - {0,3} * y^2 = 1 for x = {1,27:n0} and y = {2,25:n0}", n, x, y);
}
}
}
- Output:
x^2 - 61 * y^2 = 1 for x = 1,766,319,049 and y = 226,153,980 x^2 - 109 * y^2 = 1 for x = 158,070,671,986,249 and y = 15,140,424,455,100 x^2 - 181 * y^2 = 1 for x = 2,469,645,423,824,185,801 and y = 183,567,298,683,461,940 x^2 - 277 * y^2 = 1 for x = 159,150,073,798,980,475,849 and y = 9,562,401,173,878,027,020
Go[edit]
package main
import (
"fmt"
"math/big"
)
var big1 = new(big.Int).SetUint64(1)
func solvePell(nn uint64) (*big.Int, *big.Int) {
n := new(big.Int).SetUint64(nn)
x := new(big.Int).Set(n)
x.Sqrt(x)
y := new(big.Int).Set(x)
z := new(big.Int).SetUint64(1)
r := new(big.Int).Lsh(x, 1)
e1 := new(big.Int).SetUint64(1)
e2 := new(big.Int)
f1 := new(big.Int)
f2 := new(big.Int).SetUint64(1)
t := new(big.Int)
u := new(big.Int)
a := new(big.Int)
b := new(big.Int)
for {
t.Mul(r, z)
y.Sub(t, y)
t.Mul(y, y)
t.Sub(n, t)
z.Quo(t, z)
t.Add(x, y)
r.Quo(t, z)
u.Set(e1)
e1.Set(e2)
t.Mul(r, e2)
e2.Add(t, u)
u.Set(f1)
f1.Set(f2)
t.Mul(r, f2)
f2.Add(t, u)
t.Mul(x, f2)
a.Add(e2, t)
b.Set(f2)
t.Mul(a, a)
u.Mul(n, b)
u.Mul(u, b)
t.Sub(t, u)
if t.Cmp(big1) == 0 {
return a, b
}
}
}
func main() {
ns := []uint64{61, 109, 181, 277}
for _, n := range ns {
x, y := solvePell(n)
fmt.Printf("x^2 - %3d*y^2 = 1 for x = %-21s and y = %s\n", n, x, y)
}
}
- Output:
x^2 - 61*y^2 = 1 for x = 1766319049 and y = 226153980 x^2 - 109*y^2 = 1 for x = 158070671986249 and y = 15140424455100 x^2 - 181*y^2 = 1 for x = 2469645423824185801 and y = 183567298683461940 x^2 - 277*y^2 = 1 for x = 159150073798980475849 and y = 9562401173878027020
Julia[edit]
function pell(n)
x = BigInt(floor(sqrt(n)))
y, z, r = x, BigInt(1), x << 1
e1, e2, f1, f2 = BigInt(1), BigInt(0), BigInt(0), BigInt(1)
while true
y = r * z - y
z = div(n - y * y, z)
r = div(x + y, z)
e1, e2 = e2, e2 * r + e1
f1, f2 = f2, f2 * r + f1
a, b = f2, e2
b, a = a, a * x + b
if a * a - n * b * b == 1
return a, b
end
end
end
for target in BigInt[61, 109, 181, 277]
x, y = pell(target)
println("x\u00b2 - $target", "y\u00b2 = 1 for x = $x and y = $y")
end
- Output:
x² - 61y² = 1 for x = 1766319049 and y = 226153980 x² - 109y² = 1 for x = 158070671986249 and y = 15140424455100 x² - 181y² = 1 for x = 2469645423824185801 and y = 183567298683461940 x² - 277y² = 1 for x = 159150073798980475849 and y = 9562401173878027020
Perl[edit]
sub solve_pell {
my ($n) = @_;
use bigint try => 'GMP';
my $x = int(sqrt($n));
my $y = $x;
my $z = 1;
my $r = 2 * $x;
my ($e1, $e2) = (1, 0);
my ($f1, $f2) = (0, 1);
for (; ;) {
$y = $r * $z - $y;
$z = int(($n - $y * $y) / $z);
$r = int(($x + $y) / $z);
($e1, $e2) = ($e2, $r * $e2 + $e1);
($f1, $f2) = ($f2, $r * $f2 + $f1);
my $A = $e2 + $x * $f2;
my $B = $f2;
if ($A**2 - $n * $B**2 == 1) {
return ($A, $B);
}
}
}
foreach my $n (61, 109, 181, 277) {
my ($x, $y) = solve_pell($n);
printf("x^2 - %3d*y^2 = 1 for x = %-21s and y = %s\n", $n, $x, $y);
}
- Output:
x^2 - 61*y^2 = 1 for x = 1766319049 and y = 226153980 x^2 - 109*y^2 = 1 for x = 158070671986249 and y = 15140424455100 x^2 - 181*y^2 = 1 for x = 2469645423824185801 and y = 183567298683461940 x^2 - 277*y^2 = 1 for x = 159150073798980475849 and y = 9562401173878027020
Perl 6[edit]
sub pell (Int $n) {
my $y = my $x = Int(sqrt $n);
my $z = 1;
my $r = 2 * $x;
my ($e1, $e2) = (1, 0);
my ($f1, $f2) = (0, 1);
loop {
$y = $r * $z - $y;
$z = Int(($n - $y²) / $z);
$r = Int(($x + $y) / $z);
($e1, $e2) = ($e2, $r * $e2 + $e1);
($f1, $f2) = ($f2, $r * $f2 + $f1);
my $A = $e2 + $x * $f2;
my $B = $f2;
if ($A² - $n * $B² == 1) {
return ($A, $B);
}
}
}
for 61, 109, 181, 277 -> $n {
my ($x, $y) = pell($n);
printf("x² - %3dy² = 1 for x = %-21s and y = %s\n", $n, $x, $y);
}
- Output:
x² - 61y² = 1 for x = 1766319049 and y = 226153980 x² - 109y² = 1 for x = 158070671986249 and y = 15140424455100 x² - 181y² = 1 for x = 2469645423824185801 and y = 183567298683461940 x² - 277y² = 1 for x = 159150073798980475849 and y = 9562401173878027020
REXX[edit]
/*REXX program to solve Pell's equation for the smallest solution of positive integers. */
numeric digits 2200 /*ensure enought decimal digits for ans*/
parse arg $ /*obtain optinal arguments from the CL.*/
if $='' | $="," then $= 61 109 181 277 /*Not specified? Then use the defaults*/
d=22 /*used for aligning the output numbers.*/
do j=1 for words($); #= word($, j) /*process all the numbers in the list. */
parse value pells(#) with x y /*extract the two values of X and Y.*/
say 'x^2 -'right(#,max(4,length(#))) "* y^2 == 1 when x="right(x, max(d,length(x))),
' and y='right(y, max(d,length(y)))
end /*j*/
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
floor: procedure; parse arg x; _= x % 1; return _ - (x < 0) * (x \= _)
/*──────────────────────────────────────────────────────────────────────────────────────*/
iSqrt: procedure; parse arg x; r= 0; q= 1; do while q<=x; q= q * 4; end
do while q>1; q= q%4; _= x-r-q; r= r%2; if _>=0 then do; x= _; r= r+q; end; end
return r /*R: is the integer square root of X. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
pells: procedure; parse arg n; x= iSqrt(n); y=x /*obtain arg; obtain integer sqrt of N*/
r= x + x
parse value 1 0 with e1 e2 1 f2 f1 /*assign values for: E1, E2, F1, F2. */
z= 1
do until (e2 + x * f2)**2 - n * f2 * f2 == 1
y= r * z - y
z= floor( (n - y*y) / z)
r= floor( (x + y ) / z)
parse value e2 r * e2 + e1 with e1 e2
parse value f2 r * f2 + f1 with f1 f2
end /*until*/
return e2 + x * f2 f2
- output when using the default inputs:
x^2 - 61 * y^2 == 1 when x= 1766319049 and y= 226153980 x^2 - 109 * y^2 == 1 when x= 158070671986249 and y= 15140424455100 x^2 - 181 * y^2 == 1 when x= 2469645423824185801 and y= 183567298683461940 x^2 - 277 * y^2 == 1 when x= 159150073798980475849 and y= 9562401173878027020
Sidef[edit]
func solve_pell(n) {
var x = n.isqrt
var y = x
var z = 1
var r = 2*x
var (e1, e2) = (1, 0)
var (f1, f2) = (0, 1)
loop {
y = (r*z - y)
z = floor((n - y*y) / z)
r = floor((x + y) / z)
(e1, e2) = (e2, r*e2 + e1)
(f1, f2) = (f2, r*f2 + f1)
var A = (e2 + x*f2)
var B = f2
if (A**2 - n*B**2 == 1) {
return (A, B)
}
}
}
for n in [61, 109, 181, 277] {
var (x, y) = solve_pell(n)
printf("x^2 - %3d*y^2 = 1 for x = %-21s and y = %s\n", n, x, y)
}
- Output:
x^2 - 61*y^2 = 1 for x = 1766319049 and y = 226153980 x^2 - 109*y^2 = 1 for x = 158070671986249 and y = 15140424455100 x^2 - 181*y^2 = 1 for x = 2469645423824185801 and y = 183567298683461940 x^2 - 277*y^2 = 1 for x = 159150073798980475849 and y = 9562401173878027020
Visual Basic .NET[edit]
Imports System.Numerics
Module Module1
Sub Fun(ByRef a As BigInteger, ByRef b As BigInteger, c As Integer)
Dim t As BigInteger = a : a = b : b = b * c + t
End Sub
Sub SolvePell(n As Integer, ByRef a As BigInteger, ByRef b As BigInteger)
Dim x As Integer = Math.Sqrt(n), y As Integer = x, z As Integer = 1, r As Integer = x << 1,
e1 As BigInteger = 1, e2 As BigInteger = 0, f1 As BigInteger = 0, f2 As BigInteger = 1
While True
y = r * z - y : z = (n - y * y) / z : r = (x + y) / z
Fun(e1, e2, r) : Fun(f1, f2, r) : a = f2 : b = e2 : Fun(b, a, x)
If a * a - n * b * b = 1 Then Exit Sub
End While
End Sub
Sub Main()
Dim x As BigInteger, y As BigInteger
For Each n As Integer In {61, 109, 181, 277}
SolvePell(n, x, y)
Console.WriteLine("x^2 - {0,3} * y^2 = 1 for x = {1,27:n0} and y = {2,25:n0}", n, x, y)
Next
End Sub
End Module
- Output:
x^2 - 61 * y^2 = 1 for x = 1,766,319,049 and y = 226,153,980 x^2 - 109 * y^2 = 1 for x = 158,070,671,986,249 and y = 15,140,424,455,100 x^2 - 181 * y^2 = 1 for x = 2,469,645,423,824,185,801 and y = 183,567,298,683,461,940 x^2 - 277 * y^2 = 1 for x = 159,150,073,798,980,475,849 and y = 9,562,401,173,878,027,020
zkl[edit]
GNU Multiple Precision Arithmetic Libraryvar [const] BI=Import("zklBigNum"); // libGMP
fcn solve_pell(n){
x,y,z,r := BI(n).root(2), x.copy(), BI(1), x*2;
e1,e2, f1,f2 := BI(1), BI(0), BI(0), BI(1);
reg t; // a,b = c,d is a=c; b=d
do(30_000){ // throttle this in case of screw up
y,z,r = (r*z - y), (n - y*y)/z, (x + y)/z;
t,e2,e1 = e2, r*e2 + e1, t;
t,f2,f1 = f2, r*f2 + f1, t;
A,B := e2 + x*f2, f2;
if (A*A - B*B*n == 1) return(A,B);
}
}
foreach n in (T(61, 109, 181, 277)){
x,y:=solve_pell(n);
println("x^2 - %3d*y^2 = 1 for x = %-21d and y = %d".fmt(n,x,y));
}
- Output:
x^2 - 61*y^2 = 1 for x = 1766319049 and y = 226153980 x^2 - 109*y^2 = 1 for x = 158070671986249 and y = 15140424455100 x^2 - 181*y^2 = 1 for x = 2469645423824185801 and y = 183567298683461940 x^2 - 277*y^2 = 1 for x = 159150073798980475849 and y = 9562401173878027020
