Data commit

Task/Pells-equation/Wren/pells-equation.wren

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+import "/big" for BigInt
+import "/fmt" for Fmt
+
+var solvePell = Fn.new { |n|
+    n = BigInt.new(n)
+    var x = n.isqrt
+    var y = x.copy()
+    var z = BigInt.one
+    var r = x * 2
+    var e1 = BigInt.one
+    var e2 = BigInt.zero
+    var f1 = BigInt.zero
+    var f2 = BigInt.one
+    while (true) {
+        y = r*z - y
+        z = (n - y*y) / z
+        r = (x + y) / z
+        var t = e1.copy()
+        e1 = e2.copy()
+        e2 = r*e2 + t
+        t = f1.copy()
+        f1 = f2.copy()
+        f2 = r*f2 + t
+        var a = e2 + x*f2
+        var b = f2.copy()
+        if (a*a - n*b*b == BigInt.one) return [a, b]
+    }
+}
+
+for (n in [61, 109, 181, 277]) {
+    var res = solvePell.call(n)
+    Fmt.print("x² - $3dy² = 1 for x = $-21i and y = $i", n, res[0], res[1])
+}